I'm new to the forum so sorry if I missed this while using a search. Does anybody know the differences between the 3.4DOHC and 3.1 in luminas 90-94? If I wanted to drop a 3.4 into my current 3.1, are the mounts, wiring harnesses, computers, transmission all different?

yes you would have to use everything off the donor car including the transmission,,wireing harness puter and all.