help runs like s@#%

2000 s-10 p/u 70kmiles 4.3 auto. start up in the am, pull up the driveway and starts backfiring and bucking up driveway. pulling 2000 lb trailer, just drops off and loses speed from 65 to 40 on relativly flat road. changed plugs, coil, wires, cap, rotor, fuel filter, 3 o2 sensors( as per gm dealer mechanic said bad no difference). tps voltage all good, fuel pressure stays at 55psi. running out of options, dealer cant fix either. help... am i overlooking the obvious or what??

hows the tranny doing? if you have a cooked gear, or burned bands or something like that, it would explain most of the problem...

definitly not tranny, also, when cool morning, stalls out just sitting there. when i power brake the truck, it pops and backfires also, almost anytime its under a load

I would think such radical behavior would certainly set a trouble code or two. Is your "check engine" light on? If not, I would backfire it down to my local AutoZone and have them download any trouble codes (they do it for free)..... although I'm sure the dealer must've done this(?).

Just some thoughts:

Got the plug wires connected in the correct sequence and on the right dizzy posts?

Sounds like maybe the timing (as in computer controlled) is going bonkers (with all of the back firing and loss of power at speed)

Does the engine idle smoothly?

the only trouble codes were for the o2 sensors. it idles after almost stalling a few times when it is cold. about 20 seconds, then it is fine. checked the plug wires about 10 times with a chiltons manual.

have you ever cleaned:

throttle body
EGR
IAC

?


the only trouble codes were for the o2 sensors. it idles after almost stalling a few times when it is cold. about 20 seconds, then it is fine. checked the plug wires about 10 times with a chiltons manual.

egr is a common problem. and a good thing to check.
have you checked for vacuum leaks? or pinched vacuum lines? hows you charching system? not just volts make sure you are getting enough amps. not getting the volts or amps will surly cause you problems.
pcv is also a good one to check. i usually change it out everyother tune up (cheap and easy).
its early in the morning and i havent had my coffee yet so later i could probably come up with some more ideas. i hope i have given you some good ideas and things to check in on. good luck and keep us posted.