Climbing over multiple passes under 2000', not towing or loaded, and the transmission starts slipping. I pull off at next exit and the truck will barely pull out of the stop sign to get into a vacant lot. Looked underneath and no visible transmission leaking this time, but smoking from the same area. I let the truck cool off for a bit, got back on the highway and didn't have any further issues. I took it to the dealer and they found nothing wrong.