Maybe my search criteria was not good, but I found nothing on this exact issue. 20k miles ago did a new connector sleeve and pan/filter/fluid swap. Also reset adaptations. All was well. Recently we have had some wicked cold overnight temps, -14 F or colder. Around this time I noticed that she would hold 3rd when getting on the highway. I thought maybe it was a way for both the engine and trans to warm up, this is similar behavior my BMW or Benz had (I forget which). But when cold, it would avoid certain gears until up to temp. But I do get up to temp or I should say I drive it, its plenty warm and stop to fuel. When I get back on the highway, it holds again.

Here is the oddity and temp fix. If I drop into sport mode, it stays in 3rd but I can manually shift perfectly fine. Fast but not jerky shifts, totally normal. And I can bring it right up to 6th. Once I do this I can go back to normal drive mode and it will stay in 6th or go to 5th, 4th and back to 6th as needed. Like all is well again. Its like I have to "show" it the other gears.

No codes. So today at work I pulled it into the heated shop at work and disconnected the battery for a reset. It was in there all day and got plenty warmed up. Left work, which is 1 minute from a 55mph county road, and it proceeded to hold 3rd again. I can not rule out a potential linkage issue, its been wicked cold and lots of road salt. But I do lubricate it often and the shift lever feels very smooth. Other than that, no clue.

 

Is it stuck in 3rd ? linkage wont affect gear changes as its all done via the valve body and solenoids, any corrosion at the shifter pcb connection ?

 

No, its not stuck in 3rd.

 

Perform a live check with numeric display of your "pressure control solenoid driver" of 1 through 6 solenoids while driving with your GAP tool. Also set it to display "torque converter status and shift type" to see if the converter is going into lockup. Display "transmission current gear" so you can see what gear your in when the solenoids change amperage (when upshifting and downshifting). My 4.0L V6 shows 0.848a and 0.0480a depending the mode of the solenoid. If you have a bad solenoid, it'll throw odd amperages that don't match the others. I had a similar issue and found a couple bad solenoids. I replaced them all and the shifting issue cleared up and got the lockup back in the converter.