1995 5.7 GMC SUBURBAN K1500 Won't start.

95 Suburban sputters/loses power, backfires Loud, now won't start. I have a
1995 gmc suburban 5.7 350 v8 k1500, bought it in 2001 and ran perfectly fine
with regular tune ups and maintenance , never let it run with less than 1/4
tank the transmission went out and we had it rebuilt by AAMCO, when we got
the trick back it would shift from park, AAMCO fixed that and it ran perfect
until the middle of May when it is at operating temperature (200-210) it will
sputter and lose power when accelerating from any speed if we press the gas
to fast, if we ease of te peddle when it is sputtering and losing power, the
Rpms go back to normal and truck runs fine if we don't accelerate normally.
When accelerating it will sometimes sputter an backfire really loud, it shouts
black smoke from the exhaust and dies, it starts right up an will continue to
repeat this as we drive unless we speed up talking 10 seconds to get to 15
mph. Replaced the muffler and catalytic converter, mechanic said muffler was
full of all the crap that was in the catalytic converter. Run fine for a few hours
but problem persisted. Truck runs fine when it's first started speeds up
normal, no sputters or backfires and can get and stay at 75 mph until it's
warm then starts sputtering as we try to accelerate backfires and dies, when
we restart it from backfiring an dying it sounds like metal clanking from
underneath the truck, like gears or something getting back in motion, but this
is not heard when it is stopped and started like normal. Yesterday it was
running fine like always until about 20 or 30 minutes after starting it and
driving all highway it died on the freeway and now will not start. Replaced fuel
pump, fuel filter, spark plugs, rotor and distributor cap, cleaned egr valve. The
last thing we did to it was the plugs cap and rotor, all other maintenance I
mentioned was performed while the truck was running.