2004 2500HD Diesel surges between 55-60

[Justusgirls]

This actually started last fall and continued into the spring then just quit. So I thought but, as cold weather is coming back so is the problem.
This problem only occurs between 55-60mph and going downhill, no matter how slight. If I accelerate at all, it goes away.
I first noticed it with my cruise on and thought the cruise was confused as whether to accelerate or not. Since we live off a state highway I use my cruise a lot. Then one day I discovered the cruise had nothing to do with it.
I have had the truck to 3 different shops and a transmission repair in the area. No code is ever set. Everyone has a different opinion of the issue but one thing they all have in common is they do not know what the problem is. After experiencing it they tell me they have never dealt with a issue like this before.
I would like to get it corrected but I am stumped as well.
Anyone ever experience this before?

[4x4toy]

How is the idle? Does it have a slight surge when sitting still with brake applied, like sitting at a red light?

[MadManAndrew]

Join a Duramax forum. Todays turbodiesels are very different from gas motors, you'll get much better help there. I use Dieselplace.com.