I have close to 2 gallons on my XL and have yet to have an issue with the transmission. Only issue I had at first was when I disassembled it to look at examine everything, there was an excessive amount of lock-tite on one of the clutches and I broke one of those little flanged bearings trying to take it apart! I had HPI warranty it though.
I have a LRP30 in mine with 16/47 gearing at the time, so that is considerably higher than stock, and I haven't had anything happen to the transmission.
For Halloween I have the Jumbo Kong wheels on it with 14/52 gearing, so I'll see how the transmission holds up to that.
