2001 Dodge Dakota - Over Drive turns off on steep slopes?

[Joesph B]

I have a 5.9 V8 Dodge Dakota,with about 60k miles on in. We have a house in the mtns when i drive my truck on the Hwy i can do 70 and the truck runs fine. But when i start up the grade to go up the mtn my O/D turns off... I had my Trans Temp light come on once but i did a flush and it has come back on since just the O/D turns off ... any ideas?

 

[mike]

i think it is normal for od to turn off when going up an incline