2010 RL shaking during acceleration at high speed
 

My 2010 RL (SH-AWD) with 82K miles began shaking when accelerating after driving about a 1/2 hour at freeway speed (65-80mph). Driving back from destination after it cooled for several hours it repeated the problem after about a 1/2 hour of driving. Same problem occurred after long test drive this am. There's no evidence of the problem when cool or driving under 50mph.

I pulled the wheels and there's no wheel bearing noise of or difference in resistance between all 4 wheels when spinning wheels. There's no clunking or grinding coming from CV joints when driving straight or turning. The car had its torque converter replaced at 63k miles (under warranty) and all differential and transaxle fluids were serviced with Acura AWD fluid at 35k and 75k miles. Any ideas?