Problem update, resolved! Sorry for the delay as I have been out of the country. Thanks to all for the input.
FreeScan indicates 82C, I suspect I did not wait until the engine was warm on my first go at this. Water/engine temp is not the problem.
I thought the engine sounded different when this problem first happened, now that I am back in town and at it again, I am certain the engine/turbo sound is not right. When hitting the current maximum boost, I am certain I can hear an air pressure loss. It is a sort of "whoosh" that stops instantly when I back off the throttle. It had more of "pop" before when backing off the throttle. So at first I focused on the dump valve.
I finally noticed a clamp on the air hose between the ChargeCooler and the intake manifold had slipped from position. In fact it slipped off the hose and the hose was not secure on one end. You might think this was easily spotted, but it wasn't. Everything was in position, but the clamp was just off the hose slightly and barely noticeable that it was no longer on the hose. Simply, at high boost the pressurized air leaked out between the Charge Cooler and the manifold. Jim as Lotsu s4s was bang on, it was a turbo hose! Thanks Jim, I re-read all the posts as well as yours and started looking very close.
The car is near mint and the engine bay very clean. I had the car on exhibit at a car show early and had sprayed all the hoses with tire silicone for a high sheen. It made the hose slippery and I gather at high boost the hose pressurized, inflates a wee bit and pushed the clamp off the end. Fluke! The roads are still wet so I can't take it for a test drive, but for sure this was the air leak and the sound of the "swoosh" and lack of "pop" when I back off the throttle. Image below highlights the clamp that slipped.
Next day update, dry today and got the Lotus out to confirm full boost is back. Many hours to determine the cause, minutes to repair. Again, thanks for the input. This forum rocks!
Ron