I have a 2000 Venture with 165,000 miles and it started to act like it as down shifting at around 43 mph and after a while it will start a whinning noise. Also noticed a derease in MPG and the engine sounds like it is running at a higher RPM. Took it to a Tranny shop and he connected the computer and we drove around for about a 1/2 hour. No codes and most everything within normal operating paramaters except an occasionalslightly elevated clutch lockout. RPM if I remember correctly was 2100 on the Hwy. Fluid was changed at 80,000. Fluid appears and smells fine. Added Lucas transmission repair 3 weeks ago.....no change. Any suggestions?