I learnt the hard way in how valuable an oil cooler is the other day in my Jeep. Going over a big set of hills, just started blowing smoke. Didnt loose any function in the box to begin with. Now it doesnt have 4th and reverse is almost gone. It did something similar to yours about a year back, thought it was a computer problem, swapped it out and didnt have a problem until the gearbox blew its load everywhere.