Two problems related to speed sensor have been reported for the 2008 GMC Acadia. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 GMC Acadia based on all problems reported for the 2008 Acadia.
Vehicle has a delayed shift into 3rd and 5th gear, with a vibration felt in those gears. Found codes p0717 p0716 for input speed sensor on transmission. It is believed the vehicle has a broken 35r wave plate and need to tare down to inspect or replace transmission at only 63,000 miles. Extremely common problem on these vehicles (please refer to GMC Acadia foums online everywhere for other victims).
I purchased the GMC Acadia from a dealership in kaiserslautern germany in may 2012. By April 2013 the transmission completely stopped working. At first the SUV would jump gears 6-3 sometimes 6-1 while moving at speeds higher than 35 mph. I have 3 young children and the result of such sudden shifting could have caused whiplash and did cause fear. I took the vehicle to auto schneider in weiden germany who identified the speed sensor as the problem via the computer and replaced the part. By 10 may 2013 the vehicle was completely immobile. I conducted research and have found over 1000 entries specifying that people have had to replace the transmission around 70000 miles, and sometimes twice, with GMC covering 0 costs. As a us service member I believe that the NHTSA should monitor complaints on other sites and investigate poor mechanics especially when tax dollars were used to rehabilitate GMC in 2008. Anytime there is a mechanical failure in a vehicle's transmission it can cause incident.