Engine compression

I have a 4x4 1990 Ford F-250 XL. I can start the truck when the engine is cold,
but after driving it for a few minutes if I shut the truck off it won't restart.
The truck won't turn over and pulls the battery down. I have had the battery
tested and it is good.

Also, I have a thirty minute drive to work. About halfway through the trip smoke
starts filling up the cab. I have noticed that the problem is coming from oil
being pumped out of the dipstick leaking down on the exhaust. I was told at my
local autoparts store to replace my PCV valve, which I did, but the problem
hasn't been resolved. They said that my problem was compression building up in
my engine. I would appreciate it if you could give me some advice.

Thanks

Jim Kraus