I've got a '99 Ram 1500 4x4 5.9 V8 with 125,000 miles. I've had it for a little over a year with no real problems. This week when I was towing my boat with OD locked out, it began shifting erratically between 3rd- 4th. Now it does it all of the time. Yesterday, I stumbled on a connection. It seems so far like the problem only happens or at least is worse when the cruise is on (not necessarily set). With cruise off, it seemed to be fine.

I've seen hundreds of posts about solenoids and pressure sensors, and almost as many that say this didn't help. I've also seen lots of talk about trans speed sensors and vehicle speed sensors. The trans doesn't slip... just seems "confused". What do you guys think?

 

If OD is off then it won't go into 4th, which is OD.

 

The speed sensor is in the tailshaft of the transmission. It sends signal to PCM, which does several things, including sending signal to speedometer. If OD is turned off, like zman said, it should not shift to 4th. And cruise while towing is not necessarily a good thing to do as the cruise control is set up to compensate for weight of truck and not with the increased load (unless really flat terrain).

If cruise power is on and not set, it really should not be a factor. Seems strange.

Check trans fluid level in neutral. See if it smells burned or appears dark. If it has been sometime, it might be able to use fluid and filter change and check band adjustment. Cleaning governor pressure sensor and solenoid would not be a bad preventative measure as well. If pan does not have a drain plug, I would suggest adding one.

 

Check for vacuum leaks too.

 

And don't forget to check the plenum.

Yer slippin' there zman. Missed your standard que in your post.

 

I dopped the pan, changed the fluid and filter when I bought the truck last year. I'm running ATF+4 full synthetic. The fluid I drained wasn't too bad. Still pinkish and didn't smell burned.

BTW, I wasn't towing with cruise on... just noticed later on that the problem seemed to be worse with cruise on but not set.

It almost feels like the torque converter locking and unlocking. The RPMs bounce back and forth between 1500 to 2000. Problem is worst between 55 and 60 MPH.

 

Check the TPS sensor. if it is getting ready to go belly up, it will give you the TCC issue.

 

And if TCC has an issue, I think it usually throws a code, but maybe not always. Doe TC lock up in 3rd?

 

TC does lock in third. I had a similar problem and the TPS was the culprit. Make sure to disconnect the batt when changing it.

 

Then I've got a question, say your going down the interstate pulling a loaded trailer, what if your running the high end of 3rd gear with OD off, would't you want the ability to shift into 4th? Or just run 3rd all the way?

Edit:

Sorry if this question seems stupid, just seems stupid to me that we lock out a gear by turning off OD.