A weird situation

[72highboy390]

04 f-250 6.0L, as of right now only bully dog gt. I changed the oil in the truck with T6 Rotella 0w40. along with oem filter. Truck would rough start everytime when cold. finally got mad and bought some sea-foam, got the engine extremely hot,(with the sea-foam for 60mins), drove home and dropped the oil, replaced with castrol 5w40 and another oem filter. Havent had the problem since.

what do you think the problem was?

[Pistolgrip426]

I'd lose the castrol before you have a major catastrophe,is that car oil or diesel oil ?