Last week I put in the stall I have had on the shelf for a long time. It is a used yank tt2600 that I got from a member here.

I have an 02 yukon denali awd, stock trans/pcm. I do have a big B&M 13x10 trans cooler.

I drove it around town for a couple days and all seemed normal. Lockup characteristics seemed normal as well, although I never got above about 55-60mph.

Couple of days ago I had to take a road trip about 300 miles away and tow a car back, something I've done many times with this truck.

On the way down (unloaded) I noticed the converter would not want to lock up at highway speed, 70-80. I rode for 20-30 miles at a time and it would not lock. Obviously the trans would heat up as time went on, but it never got over about 200. If I slowed down to around 60mph for a couple of minutes, it would eventually lock up (it was hard to tell when exactly it happened since I was watching the traffic I was behind).

Once it was locked, it tended to want to stay locked without a considerable amount of additional throttle...maybe a bit more than I usually have to apply to unlock it, or maybe it just seems that way because i am getting used to the response of the new converter? It would stay locked up for 20-30 miles and the trans temp would come down to 140, and then randomly unlock again for 20-30 more miles and it would slowly rise to 200. It seemed to unlock when I had to let off the throttle totally to decelerate for traffic or going down a grade.

On the way back, in tow/haul mode towing the car, it acted the same, but was even harder to get it to lock up. The trans never got over about 230 before I was finally able to slow down to 55 for a while and get it to lock up, then it would stay that way until it cooled back down to 150, then it would unlock again and stay that way for a long time.

When I got close to home, I switched tow/haul back off while still towing, and the lockup seemed to be working more normally. In fact it would lock up and not want to come unlocked until I gave it enough throttle to kick into 3rd gear. Then when I let it go back into 4th, it would lock up within a couple of seconds and stay.

From what I have read, there are a couple of possibilities:

1) something is wrong with the lockup clutch in the converter, which could cause damage to the transmission as well.

2) the pcm needs a tune to redefine the lockup speed settings.

Or perhaps the PCM needed all that time at highway speed to "learn" the new lockup characteristics? Doubtful, but I figured I would throw it out there.

Also, I've read that a shift kit/servo should be installed with a stall. I guess the WOT shifts seem slightly softer with this stall, but nothing to write home about. I wouldnt mind installing a shift kit IF I were assured that the truck would not shift like a corvette in traffic. I tow stuff and haul the family around in the truck and want to maintain the luxury truck feel. Anyone have input on that subject?

Thanks in advance.

 

You need a shift kit and tune IMO.

The shift kit Id do with any aftermarket converter, or even a stock one for that matter.