1994 Cadillac Fleetwood cranking

Had a new key made and car would not recognise key, it started being hard to crank, when cranked would run on 4 cylinders for about 20 sec then other 4 kick in. Had computer reprogrammed to recognise key security light went away but the cranking part stayed the same, and it also shuts off while driving from time to time, anytime u restart, it starts on 4 cylinders again and the other 4 kick in and runs grate I was told by teck it needs a tune up but after it runs on all 8 cylinders it does not skip or not have power. Has good power. Another thing to crank u have to turn it over several times before it finely starts on the 4 cylinders. Thanks richard