I have a 98 ctd with auto tranny, The last week I have noticed that after I warm the truck up and drive about 10 miles the tanny shifts fine but after that it doesnt want to shift into OD or TC lockup until I go over 50 mph. would it be my TPS or is my tranny coming to an end.

 

Check your battery cables. The electronics on the overdrive trans are real sensitive to corroded battery terminals and battery cable connection at the block. Tps is something to consider as well.

 

I wouldnt want mine to go into over drive until over 55 m.p.h. anyways. actualy I dont push the button til 65