loss of power "check engine light on

Sounds like the techs are taking the usual throw parts at a problem since the customer is footing the bill. The 8.1 engine does have a rev/speed limiter that will shut things down if your speed exceeds a certain speed or your engine rpm's exceed a certain rpm. The exact limit is programmed in to your electronic control module when the engine is set up for your coach. When this happens, you will get a check engine light but after you shut the engine off and restart it, the check engine light will be off. On my coach the speed is limited to 78 MPH and I think the RPM is limited to around 4500. I've hit the speed limit shut down but never gotten to the RPM limit.