Vehicle: 2011 3500 Silvarado 63K miles, 6.6 Liter PTI Turbo Duamax Diesel with Allison Trans - original owner, no past problems.

Issue: While in slow traffic on the freeway the Engine Light came on. The underscore under "D" for Drive disappeared. I heard/felt a small clicking noise under dash, each time my foot came off the brake. As traffic speeds picked up, I noticed very little power going forward (Limp Mode?) and I had to stop at the shoulder of the road. Engine running fine, and I can shift into P, R, N, D, etc. but the truck will not move. While waiting for a tow, the message center displayed "Shift inhabited select N to Reset". The Engine Light is now off. I don't have any code numbers.

Anyone know what is happening here??

No clue without any codes pulled from the vehicle.

Dealership reports code P0700. Upon arrival at the dealership Friday (towed in), the truck was still running rough in idle. No engine light. But today, they are able to drive it with no issues. Thoughts??