OK everyone that responded, Thank You.
I found a used TB on Ebay ($!119) which should deliver next week. Mechanic did a diagnostic (2 days worth) last week and confirmed it is the integrated TPS, They have had poor success with aftermarket (Cardone, Dorman, etc which sell for $300+).
In review, it seems the problem usually happens after driving under a sustained load such as pulling a long hill and then coasting while going down the other side. DTC 's set is CEL, stability control, and reduced engine power (limp-mode). Interim solution is to keep my cheap Harbor Freight code reader handy and clear the code which takes it out of limp-mode and then the car runs fine. Once the replacement TB arrives I will RR.
I'm curious to how many Series 3 3800 owners out there with high mileage (>200K miles) have NOT had this issue. Anyone with +300K miles??
Thanks again!