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I have a 3865 and all the updates have been installed. This is my wife's truck and has been babied since new. Truck runs like new, just hoping to eek a few extra mpg with the tuner.

Problem is when I install the Mileage XS, Proformance 91 or the Tow Tune the truck's transmission will engage normally, but after driving a short distance and stopping it's like it's stuck in some higher gear and will rev and barely move. The transmission will re-engage after I press the tow/haul &H. Returned the ECU to stock and it shifts wonderfully again. Thinking it might be a fluid filter problem (only 18K since it was last done) I went ahead and changed them out yesterday. Still the same problem with tuning installed. Called Chris in Customer Service and he had never heard of this condition and frankly didn't seem too eager to find a solution (I'm sure he's a nice guy, just overwhelmed with the question).

I'm taking it to the dealer this morning to make sure the TCM has been updated to the latest software for the truck. I'm returning the vehicle to stock prior to the dealer.

This truck is totally stock with no modifications. I did use the tuner to adjust wheel size to 30.25 to better match the speedometer to the true speed on the gps (Durangos were/are notorious for showing 5% faster on the speedo than the true speed).

Any and all help would be appreciated.

Update. After spending 115 bucks at the dealership, my computer was updated to the latest software. When I returned home I installed the Proformance 91 tune. So far the symptoms have dissappeared. Later on I'll install other tunes and adjust the wheel size to make sure everything is working as it should.

**Have tried all except 87 Octane tune and it's running perfect. Even adjusted the tire size with no problems. 91 tune...holy crap, hope my wife doesn't get a lead foot.

Long story short, if you have a problem simular to mine, take it to the dealer for the updates. Good luck.

Thank you for the post, I will direct people with the same type of issue to the post.

Ron

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I have installed and ran all tunes with no problems what-so-ever. Hope this post helps someone in the future!