^^^ agree you need the harness from a manual trans 95 camaro, not sure if it will need to be a v6 harness. is the computer re burned or changed to match a manual trans. im not sure how it will react to not getting the readings from a manual.
The 95 3800 was GMs first fully compliant OBD2 Fbody. Trying to use a 3.4 OBD 1.5 harness would be a nightmare; the ignition system and even the firing order are different. The 95 and 96 PCMs are hard to flash and most tuners will not mess with them. To add to the complication GM did not make a 3800 5 speed in 95.
Motor should run your just going to set the check engine light with a bunch of tranny codes. Talk to a local tuner he may be able to tune out those codes. I am not sure why most tuners do not like the 95-96 boxes but maybe switch the PCM to not report tranny codes is doable? If you could get the codes turned off you could just terminate the wires to the tranny. The other option would be to swap in a 96 or 97 harness and PCM. Problem is since there was only about 5000 95 3800 made there is no real info on what is compatible and what is not.