Stalling engine

I have a 1986 Chevy c10, me and my dad
have been restoring it for almost 4 years, and
had the occasional Chevy oil leak, so one
night I drove it like a dumbass and blew the
engine, we eventually swapped it with a 6.0
vortex out of a 2001 Chevy 1500HD and kept
the TH350 turbo trans, we stripped down the
wiring harness down to 5 fuses and 2 relays,
engine runs sound at idle, has no problem
starting up, has a maf, no catalytic
converters, o2 sensors that go before the
catalytic converters that I don’t have,  and
new fuel pump supplying 60psi of fuel to the
engine, and new spark plugs and wires, my
issue is when I want to floor it, the engine
drops, sputters and backfires like hell, but
when I baby the gas pedal it’ll go smoothly.
My issue is it takes a solid 5 min for me to
get above 35 mph, and I’ve almost got into
multiple wrecks in a truck with no airbags.
Anything will help please, my dad and I are
stumped.