During an offroad trip this weekend , while in 4 low the truck started smoking blue smoke (oil) It d id not smoke on the way there which was an hour ride. It did not smoke on the way back .when Isay smoke haha it was bright blue. I checked the pPCVvalve it's good. What else would make it smoke intermittentl? I hhave done no test as of yet. Let me know your thoughts

 

Have you pulled the plugs and see if any are oil fouled?