Service engine light comes on after inclines

I have an '86 Buick Lesabre Limited. Recently, I having been getting a service engine soon light after taking a steep incline on my way to work. There also seems to be a loss of some power as well as hesitation on acceleration like its not getting enough gas. Belts, hoses, wires, filters, etc. have been checked and changed if necessary. It has also started stalling on occasion. I have no other ideas about what to do. It does not stall, hesitate or flash the warning light all the time, i'm really beginning to get annoyed. Any help would be appreciated.

this is the pre-series 1 3.8V6. I have no knowledge there. Fuel filter maybe?

The best way to go around this one is to pull the codes out of the computor. Jump the ALDL connector ( A & B terminals) which is under the driver side dash and turn the ignition on. Read the number of flashes the service engine lite flashes and post it here. It will flash the code 3 times and will start with code 12. The codes will lead us to the direction of your problem. Some vehicles have an EGR valve, and if yours has one, it may be weak, plugged, and/or sticking.
Good Luck.