I went up a 5-10 mile long hill at 70 mph in third (shifter in third) with the cruise control on. After it leveled off and I started downhill, it would not shift into overdrive, despite my having moved the shifter into overdrive. After a few more miles, I finally got it to go into overdrive and it has functioned normally ever since. I pulled over as soon as I could and checked the transmission fluid and it looked ok, didn't smell burnt, and was at the right level. Is this a precursor of things to come? I seem to remember reading somewhere about it not being uncommon to lose overdrive in these transmissions.

 

first of all, do not run your cruise control while limiting your trans to 3 speeds or running up a grade. You are putting your drivetrain through a lot of strain that way. 2ndly see if it might have had something to do with the cruise by running up that same grade in 3rd without the cruise on. Remember there is no real trans cooler outside the crappy useless one inside the radiator. when the radiator gets hot, the cooling capacity for the trans in reduced just as the heat in the trans builds due to the strain...I am not sure if these trans still use a vaccuum solenoid or not, that may also provide for 3-4 shift issues

 

I agree the transmission could have gotten too hot.

I usually try not to run 3rd over 55mph

 

Well, I won't be doing that again, that's for sure. I thought it would cause more heat/stress on the transmission if it were shifting in and out of overdrive often. It stayed in third the whole time up the grade. I know when I had Dodge Rams the computer would prevent them from shifting into overdrive if the transmission was too hot. Hopefully that's all it was and there's no permanent damage.