Is your 5th gear popping out? If so, there is a nut on the end of one of the shafts that holds the gears on (I know nothing about tranny internals, if this makes no sense please say something) and this nut comes loose. I have heard of people having problems with other gears popping out also though.
If you take the end cap off your tranny (the one behind the passenger's side wheel) that end cap is right where you need to look. There are a few threads on this on DSMTuners, and a write up on vfaq. If you can catch it before it trashed the transmission, you can save yourself a good amount of money and labor. I wasn't so lucky with my first transmission.
This happened to my 1st tranny in my 1g, except the nut in mine just sheared right off. Every time I show the nut to people and tell them what it is, they just look baffled and say they have never seen such a thing happen, so that was apparently a pretty rare occurrence.
DSMTuners thread:
http://www.dsmtuners.com/forums/newb...d-already.html
VFAQ:
http://www.vfaq.com/index-main.html (click 'shifter' > 'Shifter movement fix')
Side note: When I talked to TRE about the 11% taller Galant 1st gear, he did say it was physically thinner in diameter, I don't remember if he said anything about it being weaker though. 11% equates to about 4mph in 1st gear at stock redline of 7k by my math though if you were wondering how big of a difference it makes speed wise. (34.4mph vs 38.184mph in 1st gear with 7k redline) I used
this thread for my calculations.