First a little history of the truck - Bought new in 2006 used for towing work trailer (about 5K). Has 148,000 miles on it, 95% with trailer. Edge never used higher then level 2 while towing and never tried above level 3.

Transmission has been running hotter then normal for the past couple of weeks, around 185 highway and 200 around town. I have to lift on the pedal to get a 3-4 shift but then it locks and pulls hard. It will unlock dropping out of overdrive. My problem is using the Tow/Haul Mode, it will not unlock dropping out of 3rd. Truck shakes and I have to put it in neutral to unlock it. Same thing happens with the lever in 2nd gear.

Just did a fluid/filter change today and also replaced the gov solenoid (GM Type) and transducer. Fluid was a little dark but not bad and the magnet had some sludge (no large shavings). Test drove shifted a little better but same problem with TC.

What can be causing this? I searched the threads and internet, can not find an answer.

 

On my friends 98 the torque convertor would stay locked and it turned out to be the wiring harness going to the trans. It wouldn't hurt to inspect it.

 

If the trans is downshifting the the lockup circuit is releasing, the trans will not downshift if the lockup solenoid is engaged.

Whether or not the clutch is releasing is another story.

Since the 06's have a history of TC problems that would be my guess. At the very least you need a new TC.