Cummins loses power

possible loss of fuel pressure, or high pressure injector pump on the way out.

I had a turbo sensor on my Ram go out that had th same symptoms, except it wasn't intermittent. When to a Cummins truck repair shop and it took about 4 hours to isolate and diagnose.

we had that problem, 4 shops later found a 3rd fuel filter inside the door where the coach air conditioner compressor,dryer is located

This sounds like an electrical or computer problem. Zero boost for a period of time and then regaining the boost necessary to travel at speed doesn't sound like a hole in the turbo charged air system. It doesn't sound like a fuel filter either. If the fuel filter were plugged, it would remain plugged.
If your Cummin's is like mine and it sounds like it is, the primary fuel filter could be working intermittently. Even when it quits working the secondary will suck fuel through it but not at a rate necessary to run at speed.
Like other, I think your going to have to resort to having someone pull codes.

X2 on fuel filter. With a Cummins that is the first place to look.

The standard first fix for loosing power is change the fuel filters. My take is that the engine is de rateing due to generating a fault. Change the filters and if that does not fix the problem find someone who can read the engine codes fast.