i have a 93 chevy 1500. it has a 350 tbi, a 4L60e trans.
i bought a rebuilt motor with 9.5:1 compression.i bought new aftermarket heads with 2.02 intake 1.70 exhaust and  64cc

when i start the motor it runs a little rough, it takes about 2 minutes then kicks the rpm from 400 to 1000. it will run all day in park and sounds fine when giving it gas.  when u put it in drive and sit there it will die in 15 sec.  when u drive the truck i can only push 1/4 way on the gas, any more the truck will hessiate and backfire.

do i need to do anything with my computer since its not the stock motor and compressin. need help thanks  

I had a similar problem, I changed the tps (throttle position sensor) and it went away. Easy $20