L322 Restricted performance

Morning All, driving my L322 2010 3.6 V8 and it seems that on going above 55-60 mph for any length of time it soon goes into restricted performance mode. Pulled over switched off and all is fine again as long as I keep it under 55mph.. I'm about to service it and replace the rear height sensor as it's faulting anyway buy is there anything else I need to be looking at ? Some say EGR ?
Thanks

Just wondering if this could be another version of the crankcase breather filter issue I had. Although mine was the opposite issue, she wouldn't come out of cruise control.

This was the problem ..induction hose split on the top of the engine ..one of two pipes..£36 later she's a happy puppy..