Anyone that has ridden a TRX450 knows how much the back end likes to buck and how tippy a stock machine can feel through fast turns. There are 2 simple remedies for both of these.
As for the bucking, the rear shock on the TRX is in such a position that it has bad rebound, no matter how you adjust the shock. A simple fix is a new rear linkage from GT Thunder. This linkage will actually put the shock in a more vertical position which is the optimum angle for the shock to work. You will get about .5-1" lower ride height in the back which also means unbelievable handling. It is amazing what the stock shock can do when it is in the correct position.
For the Tippy feeling, it is actually the Dunlop Tires. Switch to a tire like the Holeshot or the Razr and the pushing through turns and catching the edge of the tires is completely eliminated.
A properly setup suspension will shave more seconds from your lap time than a completely built motor.