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Discussion Starter #1 (Edited)
I’m sorry this is such a long post, but I’d really appreciate any input on this issue that I’ve been dealing with since early January.

2015 2500HD. Bought new in March of 2014. In April of 2015 I bought the SPADE Duramax tuner and loaded the 40 HP tow tune. At this time I had about 15k miles on the truck. Ran that tune until July 2018 when my emissions systems took a crap. So, did the full delete and bought the 5 tune bundle with Ez-lynk from GDP Tuning (Gorilla). At this time the truck had 54,600 miles on it. I installed the shift-on-the-fly switch but kept it on setting 2 which is a 50 HP tow tune.
I have babied the truck since new and use it for mostly trips and to tow my snowmobiles in the winter (about 5,000 lbs) and my boat in the summer (about 13,000 lbs).

Truck ran GREAT after doing the delete and the 50HP tune (Also ran awesome prior with the DuramaxTuner). I only put on about 2,500 miles from July 2018 to December 2018.

Late December 2018 I received email notification from GDP Tuning that a new tune bundle was available to fix a few potential trouble codes (I didn’t have any). I loaded the new updated tunes on the truck.

Early January 2019 I leave to go on a snowmobiling trip. Drive to the Upper Peninsula of Michigan. About half way back home a few days later is when I notice a problem as follows:

Started to get a vibration/surging happening when under load at about 64 mph (6th gear) and up to the low 70's. When it happens the tach and speedometer needles both move up and down a little in unison (about 100 RPMS). It was happening more consistently in 4wd, however, would also do it in 2wd going uphill. Whenever this happens, as soon as I let up on the accelerator, the vibration stops. Also, when it's happening, if I push down more on the accelerator it also goes away. It just happens at that point of slight load/slow acceleration without downshifting. If I lock the transmission out of 6th gear, no issues at all.

I pulled up the AutoAgent App and can see the torque converter slip when this is happening and it slips from about -50 to +50 (hence the approx 100 rpm surging up and down).

In the weeks that followed I had the truck at my local shop that I trust. Ujoints good, injectors all checked out good. New fuel filter. I even had the tech ride with me and manually turn off each injector one at a time as the problem was happening and no difference. Dropped the transmission pan and fluid looked great with no metal. No metal in the spin on filter. I was able to get the problem to happen without the trailer in 4WD, however, not as severe.

I contacted GDP and they suggested trying their transmission tuning. No difference. I tried changing the Shift on the fly switch to other tunes (20 HP tune and the 100HP tune) – no difference. Then I removed the 5 bundle SOTF (shift on the fly) tunes and put the STOCK HP tune (no emissions) back on the truck and the problem is GONE. Then I decided to load just the 50 HP tune (vs the 5 bundle SOTF) and same thing, the problem is GONE. Then I tried the standalone file for the 100 HP tune… Problem gone. Then I re-loaded the 5 tune bundle and the problem is back, no matter which HP setting I’m on.

Seems like there is something wrong with that file, but how could engine tuning cause the torque convertor to slip up and down like that? Also, it’s strange that the truck didn’t act up during the first part of my Jan snowmobile trip. Although, If I remember correctly, the roads were so bad the first part of the trip that I'm not sure if I ever went fast enough for it to happen.

I will be calling GDP tomorrow since I just came to this new revelation yesterday but really wanted input from all the knowledgeable members on here.

If you read this whole thing, I thank you! I’ve been dealing with this since January 8th and have probably over 50 hours of my own time into it and many sleepless nights and just want to resolve this.
 

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i would ignore the -50 as no slip, and call it 50 rpm slip. not sure this is outside of GM specs. I personally dont like any slip in a diesel but some do.
try turning towhaul on,and do a full acceleration while watching converter slip on a scan tool.50 or less I wouldnt judge, but 100 plus is trouble.
 

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Sure sounds like the SOTF file has an issue. I've never liked the switch on the LML trucks because the power level is just trickery to the fuel temp sensor that allows a higher fuel rate and not a different tune file. I would ditch the switching tunes and leave the autocal in your truck and switch as necessary.
 

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FYI, when you have Dmax tuner non deleted tuning and you want to delete if you had called/contacted Dmax Tuner they would have referred you to their sorta like a sister tuner which is MotorOps, they would have done delete tuning for you using your Dmax Tuner AutoCal.

Can you load the original GDP tune before they screwed this up or take out the TCM tune.

Do you still have your Spade locked to Dmax Tuner, if yes, contact MotorOps.

This is how I eventually ended up with MotorOps ECM tuning.
 

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My 15 lml is doing the exact same thing, did you find a fix?
 
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