That's the same deal I had with mine.. It shifted for most of the 1st gallon of fuel though, before it started sticking in 2nd. But like you, I'd tear it down, not see anything wrong, put it back together adn it'd shift a few times and then do the same.. I had the tranny out at least 3 times before I decided to just swap it for the single speed.. Havent had a problem since, other than a broken main dogbone.. I also heard the guys who have the 2 speed and never have a problem.. Seems like if they have probs, they never seem to get fixed, but if ya get one that does good, you wont have any probs with it? I suspect it may have to do with the environment we run them in? Mine is run around sand all the time.. I think if ya have mostly hard packed dirt or asphalt, the 2spd trannys might be more reliable?I also dont know if the 1/8 scale models have issues or not?All the issues with the tranny I know of, are with the 1/10 scale..