1996 lt1 power problems

I have a 1984 blazer chassis with a 1996 lt1 camaro eng. installed . I purchased it like this.Tranny is a 700r4 which is a refirbished unit. I have a new fuel pump,fuel filter and one new fuel injector.The GM shop I took it to draind the fuel tank and cleaned the injectors.It use to run fine but it sat for a 2.5 years but was started normaly every week except the last 8 or so months due to my job taking me all over the country.----Main problem now is after it warms up it will pop and bang(back fire) and loose power when I try to acclerate.It idles fine.If I turn it off and let it sit for a few min. it will run fine for another ten min. or so and start all over again or when I come to a complete stop.At one time I did fine excess fuel in the intake tube between the throttle body and maf sensor . ---I took it to another repair shop to retreve codes from the computer , since the GM shop told me they couldnt get it to work. The problem is that there are multiple fault codes. The mechanic said that the egr was set it an open loop. I didnt not install the motor and harness myself so the person that did may have done that for some reason.The HARNESS is orginal from the camaro.----- Ive checked for exaust leaks , vacume leaks , the fuel pressure is correct and regulator is workin fine so im told. I have been told that it could be that my Frankstine's problem could be distributor.
Im very stuck and trying to fix this with the least amount of money spend , ive spent way too muc without result already .Thank for any info and help I can get .

Welcome Aboard!

I'm hoping you have a custom PCM program. The EGR can be disabled easily by disconnecting the vacuum supply to the EGR solenoid. It will probably set another code, but you'll know that the EGR is not active and opening when it shouldn't be.

Ahh, that lovely Optispark. Is your water pump leaking? When is the last time your plugs and wires have been changed? I won't rule out fuel problems until I see a fuel pressure reading. Have you changed the filter lately? It really sounds like it isn't getting enough fuel at higher load/RPM's.

no leaky water pump and no special programs. It was running fine before it was parked2.5 years ago . It has a new fuel pump and fuel filter. The mechanic I have it with at the moment is saying it has multiple faults but as I stated before i didnt put the engine in so . Im kinda at a loss there . He said all the sensors are reading ok . Said the fuel pressure is fine .He is wanting to change out the distributor. I was thinking today since I just found out that there are vac. lines going to it , that it might be the problem . It does idle fine and runs fine until it gets warm and then something goes screwy , could it be the distributor ? with the symptoms I stated earlier ? Are these symptoms of a faulty distrubtor ? Im just not sure . Im stumped and sick of giving my money away for crappy mecahnice .I would do it myself but I just dont have the equipment or the $$ to buy them right now .

Is the fuel in the tank fresh?

fuel is fresh

Was the tank cleaned and the filter changed before you put fuel in it? It's possible the pump could be giving out, unless you used a fuel stabilizer.

yea tank was draind fuel injectors were cleaned , one replaced and new pump and filter installed new fuel and ran fine for 80 miles then only a few sputters , then parked that night and the next day started to sputter again after driving ten min.when I let it sit and restart the engine it will take another ten min. to reproduce the problem . I have it at a mechanic that wants to change out the distrubtor tomorrow if the cap and rotor looks bad .I dont know if it could be the problem especially when it runs fine till its warm . I disconected the egr vac and pluged it and it still had the problem.When i first started trouble shooting this problem I did fine excess fuel sitting in the intake tube between the throttle body and the maf sensor . Im stuck 2 hrs from my house so for me to work on it is tough. What do you think about the distibutor beding the problem ???