454 engine in 91 Chevy motorhome starts and runs good until warms up then the injectors dump too much fuel and stalls engine?

I have a 1991 Chevy 30 foot motorhome chassis p-30 with a 454 engine tbi. Going up an extended grade, engine loses power, service engine lite comes on and stumbles and surges. Changed fuel filters twice, and problem seem to stop, but only to come back after approx 250 miles. Seems to happen only on a long up grade. On crest of hill and downhill, as load is decreased, lite goes off and truck seems to run more towards normal as time goes on.