put a full tank in and go from there.

The intake manifold on our trucks is 2 pieces. The belly pan gasket seals the 2 pieces. When it comes apart, it opens the intake manifold to crankcase pressure, allows oil into the intake manifold, messes up the MAP readings and fuel mileage and all kinds of wierd stuff.

 

Thanks everyone for the feedback. I think I will go ahead and replace the belly pan gasket, oxygen sensors, change oil, wires, plugs and all. It's due for it anyhow. I'll post my results.

 

For the plugs, use Autolite 3923.

O2's, use NGK's and NOT Bosch. Bosch's trip codes and are not compatible.

Servicing the distributor and belly pan gasket can't hurt. Gives you a chance to look at the lifter's, too. It's supposedly not hard.

 

I get the impression it could be the belly pan gasket, a quick search found this thread (there may be one on this site, too, but I didn't take the time to find it):

belly pan gasket

Good luck!
Robb