Hard shut off on 4.1l engine

[kcabbie]

I got this pickup a couple months back and it's been a great truck. It has some small oil leaks which will be fixed soon, hopefully. But lately it's having trouble shutting off. If feels like a diesel engine when you try to kill it. Sometime's it takes up to like 10 seconds to full cut off.
I thought it was the timming, so i took it to a shop(did not have a light) and they said it was spot on. Any other ideas? Has to be with the ignition correct? Gasoline won't combust under just pressure like diesel correct(atleast what little compression my little six banger has)?
Thanks for all help guys.