I Just replaced 5.7 vortec out of 1996 suburban and replaced it with tbi 5.7 out of 1994 Suburban which wiring harness and ecu do i use ?

You have to use the wiring harness and the OBD1 out of the 1994.

the1994

Will i need to use fuse block from the 94 or wire the 94 harness into the 96 fuse block?

You wouldn't be changing out the fuse box, you'll have to tap into some wires tho. How it all hooks up, I don't know. I have never seen anyone go this rout.

I have ben thinking about this more, your going to be better off pulling that engine out and finding a 1996 to 1999 5.7L engine to put back in there. Your just going to have a wiring nightmare, nothing but problems trying to wire that engine up. You would also have the security system to deal with.

Why would you go through all this trouble and lose a ton of power? Find the correct engine 96195hp on a good day