It seems to start out fine and then get worse over time.

 

did you ever get a chance to run the truck without the o2 in the pipe? And pull the #8 plug and look for oil fouled. 7 and 8 are the one that tend to foul with a blown plenum gasket.

 

Not yet. Hope to get to that this weekend. Thanks for the tips. Would a dealer be able to diagnose this stuff or do they shy away from the older trucks? I'm new to all this. Bought the truck for haulin stuff around. Not my daily driver.

 

The dealer will happily take your money. All of it....

Try some of the easy tests, and see what you find.