08 LMM Cruise Control Surging

[DriveAbout]

I have gone through each generation of DMax/Allison combination and this is the first time I have run into this. Currently have an 08 Sierra 3500 that has towed 9,000# trailer all over the west for over 30,000 miles. When not towing a strange speed surgeing is happening under very specific conditions. Not really a problem, but not normal. On a medium steep hill with the cruise control set for around 40MPH when the speed drops to around 38MPH there is hard acceleration all the way up to around 50-55MPH and then the throttle shuts almost all the way down and the process repeats. Going to M on the Allison confirms that this is happening in 5th gear. Any thoughts/ideas?

36,000 mile warranty is almost up so I am trying to decide if it is worth finding a seadler away from home.

[Mark Rinker]

Welcome aboard!

Can we safely assume that this truck is running the stock tune? The reason asking is I had a similar sounding surge years ago, but only when running an aftermarket tune...

If stock, my guess is a dealership reflash with updated ECM/TCM tuning will take care of your problem.

[DriveAbout]

Yes, it is the stock tune. Stock provides more than enough power for my needs. I will try and get an appointment next week so they can experiment. I am away from my regular dealer so I will have to keep my fingers crossed.