One problem related to transmission not go into gear has been reported for the 2011 GMC Acadia. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2011 GMC Acadia based on all problems reported for the 2011 Acadia.
Transmission flares out (goes into neutral) between gears when merging into highway traffic at speeds of around 45-60 mph. Most often occurs when initially accelerating to merge into faster traffic and then having to take my foot off the gas for a second or two to allow faster cars to go by, and then trying to accelerate again. The transmission is in neutral and it seems it is caught between gears (4th & 5th gears I believe) when I try to accelerate again. Engine revs to 5000 to 6000 rpm range because it is not in gear. Have to take foot off of the gas and wait a couple seconds for transmission to get into gear so I can continue driving. In the meantime faster cars are approaching as I'm in the middle of merging into highway traffic. Not being able to accelerate when merging into highway traffic creates a very unsafe situation. This issue has occurred 2-3 times a month for the last several years. Have had it looked at a number of times by gm service center but they are unable to reproduce the event when they test drive my vehicle and there aren't any special codes popping up in the computer log for them to justify doing anything to fix the problem. So they are not able to do anything about this condition.