2001 E53 - Loss of Engine power issue

[MiCkEy]

I am hoping someone can help me with this strange problem.

Sometimes from a cold start, the truck feels like it is hauling a 8000 pound trailer in the back and the "mpg gauge" is pegged all the way to the right. There is no hesitation but it does seem like something is holding the vehicle back and it seems as if the truck stays on the 3rd gear for along time with little power. This happens randomly and if I restart the truck, it's as if nothing ever happened and it drives like new. The occurrence is very random and most of the time it runs fine.

Other thing I did notice is when that happens, on a red light, the idle RPM is just under 1000 mark. When the truck runs normally its always around the 550-600 mark. Maybe this is related.

In the past I have changed the ICV, camshaft sensor, belts, water pump, fan clutch and have cleaned the MAF. Can this be the DISA valve or the MAF? There are no codes and I don't see or hear any vacuum leak or a whistling sound.