1995 Chevy Suburban Engine problem

I have a 95 or 96 motor home with a 454 engine. It has 50000 miles on the engine. It woulld not start, and was found to have a defective fuel pump. Replaced fuel pump engine started and ran fine. Drove for 25 - 30 miles without a proplem then will pullling a hill I opened the throttle fully and the motor backfired and lost all power. Engine would idle without a problem but when throttle was incresed the engine did not have enough power to pull itself. After a few minutes the problem went away and started running correctly. Again when I opended the throttle fully the problem re-occured. Took to the dealer they replaced the distrubutor, egnition module, rotor, cap. Did not fix the problem and they blamed the problem on bad gas.
I am getting bad heated oxygen senson on two sensors and it also says somthing about the crank sensor. I no longer have to fully open the throttle to cause the problem it will happen within the first 10 t0 20 miles. If I reset the error code the problem will go away until the check engine light comes on. Resetting the error will again fix the problem until the check engine light comes on. Does this sound like a crank sensor porblem? I am tired of throwing parts in an attempt to fix.

Thank you