509 camaro fan

My 90 RS 305 blew the head gaskets so I put new ones on. Also put new intake gaskets, tbi gasket, ARP head bolts, new distributor, new spark plugs, new wires, and put headers on it. I also had new exhaust from headers back put on. And a couple other things that I had a mechanic do like try and figure out why it was sputtering and driving like crap. Well at low rpm they fixed it but under load and high rpm it sputters and hesitates and the check engine light comes on and then goes off. I also had to adjust the rockers after getting the car back from the mechanic because they didn't do it. I need help because I can't drive it with the way it is driving. Maybe a sensor is going out or fuel pump. Oh it doesn't have the smog pump on it anymore put a 02 sensor on it as well. The new distributor was off of a 350 that I had laying around but was brand new...that wouldn't be the problem would it?

AlkyIROC

Under load at high rpm could be 2 things. Not enough fuel (some sort of restriction) or the ignition system is braking down. Neither of these problems could show up at lower rpm and normal driving.

You say the check engine light is coming on when this happens. What code is it setting?

509 camaro fan

Not sure about what code the check engine light comes on when it does it then turns off when it stops doing it. I was thinking possible the fuel pump or injectors are going bad. Since it has brand new spark plugs, wires, ignition coil, newer distributor on it.