If I let the truck idle while pointing downhill, it will start burning oil. Pretty good puff of smoke when I rev it up. Plenum fixed, new mopar pcv, etc, etc, etc. Valve seals?

 

I'm assuming the smoke is coming out of the tail pipe?

 

Yes, tailpipe.

 

My first thought is maybe worm valve seals toward the front of the engine. By having the front of the truck lower than the rear when pointing it downhill, maybe enough oil is pooling around the valve(s) that are worn and more oil is getting through than normal. My suggestion for testing this theory is to pull the spark plugs and see if the front ones show any indication of burning oil. Just a thought...