1995 Jeep Cherokee, HAS NO PROBLEM STARTING.

Engine Performance problem
1995 Jeep Cherokee V8 Four Wheel Drive Automatic

I have a 95' jeep cherokee. The jeep was givin to me about 6-7 mths ago. I been getting repairs done since I gotten it. (New: starter, water pump, spark plugs, wires, fuel injector and line, hose, air filter, altnator, and battery). Right before it started given me problems this last time, I had gotten gas fom luke oil which I never do (always sunoco). But the problem lies where the car start up fine with no hassle. Stays on as long as I keep it in parking gear. But soon as I take it out "p" it shuts down. Stays on in neutrul as well. It stays on if you hold down the brake and gas at the same time in drive. The check engine light is not on. What can possibly be wrong?