79 350 with tbi running rough

This is a 1979ish 4blt main 350 from a camaro or possibly a truck. The cam leads me to belive this was from a camaro. It was just rebuilt with all new bearings, crank, rings, etc. It starts up good and runs with good power but I get a constant missfire and backfiring when you let off the gas. It has a 350 esc and 350 injectors and a prom from a 1989 tbi v8, there wasn't anything other than the year written on the side of the truck at the junkyard about the actual size of the motor and the vin was gone. It's currently got 11.25psi of fuel on the in side of the tbi.

Is this something, the missfiring, that will get taken care of with a tune?