What year is your truck? Probably head gasket, but some of those timing covers would get electrolisys and eat a hole through the back of the timing cover and the water pump will puke coolant into the crank case. "If" that's the case you just need to replace the timing cover, otherwise it's head gasket time.
(and yes, you can replace the timing cover without pulling the head, but it's tricky)

not tricky at all, just drop the oil pan instead of pulling the head....make sure your very nice with the ATV sealant stuff.

yellow oil cap, you have water mixed with oil in the engine....that is not good. fix it before you hydro lock the b*tch