1990 Other GMC Models no start

Engine Performance problem
1990 Other GMC Models V8 Four Wheel Drive Automatic

1990 suburban. 5.7 auto. TBI
Cranks, and almost catches.
Sometimes catches and stumbles for a few seconds
Lots of black smoke when it stumbles
Adjusted timing, no go
Checked plugs and gapped.
Checked cap and rotor are good.
Checked for spark, lots of spark.
Confirmed all spark plug wires are routed to correct cylinder
Fuel can be seen spraying well into throttle body.
Exhaust is not plugged.
No loose vacuum lines or broken wires observed.
I am wondering if the timing chain has jumped a tooth? Only thing I have not confirmed is when #1 is at TDC if rotor is pointing at #1 plug wire.
Any other help is appreciated.