What do you mean it wont shift into drive? Overdrive??
Does it shift normaly through all the other gears?
Have you checked trans fluid? What does temperature read on trans?
If you turn tow haul off will it shift into Overdrive? It probably just wont shift into O/D with tow/Haul on, mine wouldn't at normal driving speeds, nor would it tow more than a kayak in O/D.