Hello, A few months back I bought a 2001 2500 5.9 24 valve. 150k miles, runs perfectly. Doesn't shift into overdrive, doesn't even act like it wants too. Shifts smooth into all the other gears. No bad noises, no leaks...seems perfect, other than not going into OD. What would you suggest? Thank you!

 

What makes you think it isn't going into O/D? If you hit the O/D off button, do the RPM go up?