I was digging around on here and found a thread on intake plenum failures. My truck has 250k and seems to not be nearly as strong as it used to be. I figured it was just tired but now im wondering if may be the plenum. Its a 360, doesnt smoke, uses less than a quart between changes, and purrs like a kitten. I recently put new exhaust, gutted the cat, and cleaned the TB. Im sure the stock heads are gummy and worn and figured it is just time for an overhaul. Its real sluggish in the mid to high rpm range too. Oh, and its an auto.

Who thinks this may be another plenum problem?

 

Possibly. With that many miles might as well rebuild the top end

 

and change the timing chain and gears.......

 

Remove the TB and confirm that the plenum or at least the PCV valve is not dumping oil into the intake. Your cat is gutted, so you you wont have the same symptoms as if you had a working cat.