TBI Question

I have been posting here for about a year now and have recieved some pretty good advice, but now find that I'm in need of a bit more.
spec's 91 2500 5.7, 4l80e, no air pump since the truck is 8600 gvw model.
I installed new double roller and the biggest cam the edelbrock tech recomended to still keep the computer running the 350 right, flowtech shorties, 3" catback magna flow with a high flow cat. I modified the cold air intake, "I'm not a fan of the K&N units" and after my mods I feel I'm getting plenty of GOOD FRESH COOL air, the tranny has been rebuilt with all B&M hard parts, and has been rock solid every since.
The last mod was the flowtech shorties, after the headers I noticed a big change, the difference was amazing, but now after 3 months I guess I'm getting used to the new-ness and I guess the best way to describe it is I can now really notice the limitations of the stock TBI unit, I have read posts here refering to the install of a 454 TBI unit and have been considering this mod, has anybody successfully completed this swap?
I am asssuming that the full unit is swapped not just the injectors since with more fuel there needs to be more air, will I need to install the 454 chip? if so how will this affect the rest of the componants controled by the computer, timing, sensors, etc.
my wallet always seems to be thin so I am a budget type guy though I manage to save here and there to get as good a quality product that I can, are there any mods I can do to my stock TBI to get a little more out of it till I can save for a better unit? has any one out there tried any of the after market TBI units from Holly etc? and whatwas your experience like?
I am an older carb type guy and honestly dont even know the cfm of the unit I have now or what kind of boost I can expect from the 454 unit, from looking at the TBI Id guess the stock unit I have now is not more than but maybe about what would be considered 500 cfm if compared to a carb, hoping to get up to at least 650 cfm.
Just as a side note I have been sitting on a set of vortec heads for about 4 years now going back and forth on installing them, I have the 65 cc high swirl heads on there now and they are in fair shape still, I just dont see how I could gain enough from 1 cc to justifie the swap, are they really that different in design? I have heard that they are subject to cracking and more than anything I need reliability I regularly put 1000 miles a week on my truck for work, and if not working I put a whole lot of miles on her carrying a big @ss camper and at times a boat.
any segustions /answers/ideas would be greatly appreciated, thanks.

Here's some TBI stuff I found that might help you out.

http://www.cfm-tech.com/catalog/gm_tbi_performance_parts___accessories_126905_prod ucts.htm

http://www.sportruck.com/howto/highways.htm

http://www.turbocity.com/default.php?cPath=16&osCsid=1ca9b511d2518f5f978c030781512be6

I was always going to swap Vortech heads and valvetrain onto my '95 and use the GMPP intake manifold that mates to them and still accepts the stock TBI. I also have saved magazine articles where folks used the 454 TBI to flow more air to satisfy the free flowing heads. There is also a company that hones out your stock TBI unit. Headers or left manifold from a '96 or newer is needed if running EGR for the EGR tube.

I can't imagine any benefit from the larger TB if you're still running the TBI heads. They are DEFINITELY the bottleneck that prevents good air flow in the system. They suck.

Anyway, I sold the truck before reaching this stage and bought a 6.0. If you need any information (you may already know more than I do anyway) concerning articles that I saved on this swap, I'll be glad to fax them to you.

Much Thankx for the links kylepbz, the first one gave some good info for thought.
strokes gave me more reason for consideration, I need to find out more about the heads I have on the truck now before I go changing the TBI, I will definatly be using the vortec's at some point but dont want to throw money away by installing somthing I wont be able to use with the new style heads. I know the stock heads I have now are not the greatest but I do believe they are "just" a cut above the regular 1500 or regular 2500 type truck heads, from what I have been led to believe is that on the 8600 and over gvw trucks as an option or ? there was high output engine options available, and after swaping my cam my local speed shop and dealer both mentioned that the cam I replaced was in pretty good shape and was installed in the high output engines, I bought the truck used but from what I can tell it was purchased to carry loads and the options for this were ordered, the only luxury item was A/C all other options were to make the truck more heavy duty, the suspention is massive, "sway bars, springs" etc, and I figure it was ordered for a work truck since there is no carpeting no carpet on the door panels etc.
I wish I knew more about the truck than I do.
the thing is I thought a little before I bought my cam and got one I knew I would or could use with the vortec's, I bought my headers with the o2 bung though my o2 is installed just in front of my cat so I could plumb my egr over once I installed the new heads I need to find out much more about both sets I have before I go ant further though, There is tons of write up's on the vortecs but I can'not find jack on the 65cc high swirl set I have on now, this because though I have vortec's I have the 906's not the 255'sand have heard conflicting things about the two types, and with this in mind I have also had a passing thought as to weather I should just have the high swirl heads worked over,I guess it's a case of too much info "conflicting" that is available on some heads yet not enough on other heads.
Everything I have done so far is in prep to installing a good set of heads. the heads will be the last hurrahfor me as I see it.
I installed the cam knowing my gains would be little since I retained the stock exhaust etc, I modified the cold air intake and installed headers with good gains but more than that I installed them in prep for a good set of heads, now I am researching fuel/air delivery, I'm hoping to hear from others who have already worked on this same upgrade. I will probubly stop after the heads "as long as the results are acceptable",
The spacer thing with the TBI unit is interesting, I have read conflicting posts on this, but the research of a couple of hours I have done so far has lead me to think that for the realitivly low cost it would be a good thing , at least for my application, more velosity and turning what is essentualy two separate units "the injectors" into one unit, more like a carb, as well as ballancing out fuel/air delivery, seems to me it's about the best way to make the best of the very limited TBI system that I'm stuck with, and at about 40.00 bucks it seems worth a try. As well I'm trying to find out if there is a tunable MAP sensor out there or think of a way to fool one to solve the drivability problems caused by adding performance parts and confusing the MAP.
I put this to the tech when I bought my cam, he had no answers, but back in the day if vacume was a problem , "like for the brake booster" etc. we would install a vacume canister, I cant see why this would not work for the map as well, "canister and regulate", Well I guess I have alot to research and consider, any help would be greatly appreciated, and again much thankx to Kyle and stroke for your input.