Hmmm... a clogged catalytic converter seems likely, and the ugly part is that running too long that way causes excessive combustion chamber temperatures which can crack the heads. The #8 cylinder is usually the one to go first.
Get a nice bright flashlight and an inspection mirror, crack open the throttle plates, and have a look at the belly pan underneath. If you see pooling oil you've got a failed plenum gasket allowing oil to be sucked from the crankcase into the intake.
Check for a pinhole in the oil filter. They can spew oil like mad, and this might account for the oil on the front of the vehicle where it's also being taken up into the air intake system. I mention this only because I've seen it several times and it usually confounds the hell out of people.
Compression test all eight cylinders before driving it again.
Thump on the catalytic converter with a rubber mallet. If you hear the bits inside bouncing around, the cat's a goner and should be replaced before you drive the truck again. If the cat doesn't rattle when you thump it, remove the pre-cat oxygen sensor and take a short drive. If near normal power returns, the cat's a goner and should be replaced before you drive the truck again.
Open the radiator cap (don't burn yourself) and give a sniff for combustion gases. If you smell fuel/exhaust in there, you've got a teardown coming your way.
With oil in the exhaust, the pre-cat oxygen sensor is a goner even if it's walking wounded today. Replace it as soon as the other problems are fixed. If the cat's not failed today, oil in the exhaust is killing it and it's also walking wounded toward the boneyard.
Is your CEL illuminated? If so, get the DTC's read.
Last edited by UnregisteredUser; 04-08-2011 at 08:09 PM.