I have a 89 1500 with a 350 5.7l and i poot a new 350 5.7l out of a 94 and now flames come out of inj when you start it

You either have the firing order wrong or the timing is not set right. You get fire out of the intake when a spark plug fires when an intake valve is still open. Order is 18436572 cylinders are 1357 front to back on drivers side, 2468 on passenger side. Turn the engine so the mark on the crank points to "0" on the timing scale. Set the distributor so the rotor points towards the front of the engine (not exactly but not at the firewall) If when at "0" it points to fw, turn one more time. Set wires on cap with #1 aligned with the rotor, then all others in order clockwise.
Only other possibility is that you have the valves adjusted too tight, have a bad cap or rotor or the replacement engine has a burned valve (doubt it).