Engine swap 96 Lumina now has Bucking?

It starts like a dream but when you start going uphill or over 50 MPH it starts acting like it's starving for gas. It bucks like it's out of gas. If i go over 50 and step on the gas it hesitates and starts to buck. If I slowly acclerate then it runs better? Any clues

Was the engine swapped from a like year car? It sounds like a possible trans issue, like the TCC is not letting the torque converter unlock, causing it to buck under load like a stick shift in too high a gear. Do you have a check engine/service engine soon light on?

When I left work today, my Service engine Soon light was on so I went to Autozone and the code was P1441 which is in the EVAP system. It was vague from there and it said I should go to a dealer which was a waste of time. The mechanic said it was an old car(1996) and they didn't have the codes back that far. I looked in my Haines manual and the code read "EVAP system flow during non-purge". Could it be the solenoid, the canister? I just don't know.

Probably not the bucking problem though, make sure all you evap lines in the engine compt are on properly. BTW the codes for evap are the same for 96 up, with some very minor differences, so I don't know what this " mechanic" is saying. Look around stuff you did during the swap.

I agree with Max (as I ususally do, he's a smart feller), it sounds like a vacuum or emissions system hose isn't connected properly, or you could have pinched/cracked one during the engine install (easy to do considering how many there are) . You may want to find another mechanic, because all 96 and later cars sold in the USA are required to have OBDII diagnostics, and that code is applicable to your vehicle.