95 GMC suburban 5.7 won't start no spark, sputtered backfire ran fine died

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 wouldnt 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.