if the harness is new, and it didnt fix the issue, id say its good.
might need a crank learn, some times the 3800 would set a code for it, but they always seemed to run ok. then the times they dont set a code and misfire and crap the crank learn fixes em right up.
need a tuner (hpt or efi live), or a tech 2 or the likes to do the crank learn. crazy but it takes all of 1 minute to do tops. you just set up the tuner to do a learn then e brake on, stand on the foot brake, in park and floor it to the rev limiter and let off. and its done lol