83 Coupe Deville Clunks and Dies

I drive an 83 coupe deville the the "wonderful" ht4100 engine. Ive had this problem for a while and thought it was possible a tranny problem, but i had it rebuilt and it still happens. If i drive the car around for a while the engine feels extreemly weak as if it wasnt to die. It lacks power and get up. After a while i have to b extreemly easy on the gas so that it wont die on me. If i press the gas too hard so to the floor Ill hear two pops and the engine will just die. I jsut had my tranny rebuilt, new fuel pump, and o2 sensor. What could be the problem?