if its an automatic then yes it could be a shift solenoid. also i know that in most GM automatics there is a part in the trans. that's called a reverse reaction drum and I'm sure that acura has something similar to this. when it goes bad the vehicle will only go into first and reverse so if you still have reverse that could be the problem. also if its not electronically controled there is a part called a governor that could have gone bad. either way have a good transmission shop or the acura dealership check it out first before you go and buy a new transmission