http://www.rcuniverse.com/forum/forumid_250/tt.htm
Lots of people have had that issue
There are a few creative ways to get rid of it in the HPI forum.
Some people say tune it at half a tank. Personally I've not noticed the half tank lean on mine.
best fix I seen which also moves the tank is the mid tank mod. I forgot the exacts (the instructions are somewhere in the HPI forums) but it involves modifying the radio box, and mounting an ofna tank there.