We lose power and will not go over 35-40mph, pull off road, turn off engine then restart it, no problem accelerating until it happens again-usually happens when we slow down or stop.
What causes sprinter to lose power? on 2005 Dodge Sprinter 2500
This sounds like the engine is being over revved, it is a safety built in the engine to protect it. The reason it goes away after a restart is because it is being reset automatically. Try adjusting the way you accelerate, I had to get used to this weird occurrence myself, I'm a bit of a lead foot :) Hope this helps.