engine has a miss, only when car is going up hill on 1998 Pontiac Bonneville

I've put plugs,wires, new coil pack, fuel pump and filter, gas tank completely flushed, gas cap, Car went in for service, ran good and still does, until it goes up hill. drove car about a week, after service, check engine light came on, and the miss started.

Asked by for the 1998 Pontiac Bonneville
2 answers 1 comment
Ihave same problem except i have not replaced fuel pump ,it does not occurr all the time
what was the code for the light??

Roy
oxygen sensor