Help, I need opinion

I hope someone can help me figure out whats going on with my 1988
GMC Suburban. It has a 5.7L v8. aprox 125k and has developed a
miss??. I've changed the o2,mapp,fuel filter and fixed two vacuum leaks.
The problem is not missing on one cyl but all. It seems now that I have to feather the throttle in order to pick up speed or it misses, pops
and seems to want to buck. This is especially noticible when towing
and had me wondering if I was going to reach my destination at all.
At other times it runs fine. Cranks good, idles good.
I,m reluctant to take it "in" as last time the dealer changed motor mounts to correct what was later found to be a bad u-joint.
any ideas will be appreciated.. :banghead:

check your timing. your belt may need to be replaced. Or possibly the heads are starting to wear? 3000k oil changes?

Sounds a lot like my problem... check out my post by USSCVR, "SES Lamp, Multiple Engine Misfire." Let me know if you've solved your problem.