1990 C3500 7.4L TBI backfire

[nvr2nd]

My 1990 GMC C3500 with a 7.4L backfires when cold; then seems to run with a loss of power. Occasionally backfires when warm under FOT. Truck has 192,000 miles and has just recently (within last two months) had distributor, coil, EGR valve, timing gears and chain replaced by dealer. According to dealer, fuel pump is okay. Backfire through TBI started soon after dealer' s work. Truck was originally taken to dealer because it suddenly quit running and would not start. Dealer started with idea that it was the fuel pump (check fuel pump pressure but did not change fuel pump); but then changed mind and replaced coil and when that didn't solve problem, replaced entire distributor. Truck then would run, but not for long (it stalled on the way home from the dealer). Towed back to dealer who then replaced timing gears/chain (to eliminate any timeing issues) and EGR valve (claimed carbon in EGR valve). Truck ran great for about 3-4 weeks and has now started the backfire when cold under load and seems to have a loss of power during normal freeway driving speeds (60 -70 mph). I'm the original owner and truck has been maintained very well. Any ideas of where to look next?

[maxwedge]

Many things can cause this, low fuel pressure, clogged filter weak injector, out of time, and so on, somone has to dig into this onsite for a proper diagnosis.