I have oil in cylinder #3. Mechanic believes its the rings. He says i can drive it but says he has no idea how long. Anyone have any experience with this?

If the plug is being oil fouled install a hotter plug to burn off the oil. Your mechanic should know this. You can try using a heavier grade oil. How much oil does your engine use? Blue exhaust smoke?

The truck started shaking and running poorly instantly. The check engine light started flashing as all that happened. I thought I hit a bad patch of road but that was wishful thinking. It has loss of power as well. He did diagnostics and said #3 cylinder has no compression or spark, can't remember if it's one or the other or both. When he changed plug and wire same thing and new plug was covered in oil. Haven't seen any blue smoke but honestly haven't paid attention. Only driven it short distance to shop then home. I need to limp it along for another week or two though. Trying to get the most educated answer on that. I trust my mech, he's a friend, but he's never driven with this type of issue.

If the #3 cylinder is totally dead the truck will barely run. If your friend has never run into an issue like this he must not have much experience.