96 k1500 running rough/engine codes..need help

Well first I would like to say hello to everyone here...I just joined..Ok..let me tell you what my truck is doing...96 K1500,auto,has 171,000 miles on it 5.0 Vortec.,I had done a full tune-up on it approx. a month ago..plugs,wires,cap,rotor,pcv and fuel/air filter...all the old parts were in terrrible shape..it would run a little rough,especially uphill and give me a code(#5 misfire),I bought the truck alittle over a year ago,the previous owner told me that he could not remember when he did a tune up(if at all),he owned the truck for about 8 years,but the truck ran good,now it seems the symptoms have progressed the codes I keep getting are O2 sensor bank2,#5 misfire,...it seems when the truck is cold it runs fine ,no problems accelerating..even uphill..I go to work in the morning it has no problems starting or ideling..it seems soon as it get to operating temp. if I give it a hard acceleration it starts bogging down,backfiring..mash the petal to the floor it gets worse and looses all speed,the weird thing is sometimes it wont throw the check engine light on or it will take awhile before it does..I was out on the highway and I was doing about 70 mph..lost acceleration..light came on..O2 code only(both banks)..it did that 4 times..had to pull over everytime...and it always starts right back up if I shut off the engine.. give it gas..seems to run and idle ok..start driving again and it might take a couple miles before it acts up again..the other night it gave me one code...engine misfire multi. cyli....now I know there is alot of possiblities..the injectors being one,bad cap,distributor gear...any suggestions on where to start first?..I'm thinking of replacing th O2 sensors to see what happens...I know there is talk about fuel pressure.. the fuel filter was clogged good when I replaced it..maybe its clogged again...I would really appreciate any and all suggestions on where to go from here..like I said..the problem seems to be getting worse..thanx.

02 codes do not say to replace 02 sensors.

Make sure you fuel pump and pressure is good.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Thanx MT for the info..after I made the post I went out and drove the truck...I'm beginning to feel its more of a fuel delivery problem..I checked the fuel filter it was clear.. when I cracked the lines fuel came spraying out..just for quick check I manually checked the fuel pressure at the rail..fuel came out but it seemed to be weak in pressure..no way of really knowing until its hooked up to a gauge checked..I was also thinking about the canister being clogged or bad too.. all the time I was trying to get it to throw a code and it would'nt it began stall out on me and it was difficult at times to re-start it really seemed as if it was not getting any fuel...where is the fuel pressure regulator located at?..thanx again.

Check this site out:
http://www.autozone.com/az/cds/en_us/0900823d/80/08/74/6c/0900823d8008746c/repairInfoPages.htm

Hope this helps

Thanx MT for the info..after I made the post I went out and drove the truck...I'm beginning to feel its more of a fuel delivery problem..I checked the fuel filter it was clear.. when I cracked the lines fuel came spraying out..just for quick check I manually checked the fuel pressure at the rail..fuel came out but it seemed to be weak in pressure..no way of really knowing until its hooked up to a gauge checked..I was also thinking about the canister being clogged or bad too.. all the time I was trying to get it to throw a code and it would'nt it began stall out on me and it was difficult at times to re-start it really seemed as if it was not getting any fuel...where is the fuel pressure regulator located at?..thanx again.

You are welcome.
A squirt or seemed to be weak doed not count.
You need 60/66 lbs of fuel pressure.
Go threw the fuel pressure check with a good gauge.

Fuel pressure regulator will be inside the plastic intake cover on that one.

Run the pressure check and post back results.
MT

ok...I did fuel pressure test yesterday...my friend's mechanic came by with a scan tool and fuel pressure gauge...at idle the pressure was 44-45 psi, soon as I turned it off with the igniton in the on position it dropped immediatly to 15 psi..pump is working..he told me its the regulator..did not get a chance to drive it with the gauge hooked up..the truck was acting up..I'm gonna go ahead and replace the regulator and do the injector upgrade while I'm in there..thanx for all the input guys

Do the full pump and fuel pressure test before throwing parts at it.