I think there is too much weight on the rear. Maybe you could reverse the motor and fix the steering servo on the left side of the car.

If you reverse the motor it puts the motor on the top left and the steering servo stays where it is. What you need to do is get 4 sets of scales, one for each wheel, and get the value on each the same. But if your not racing i wouldn't bother. What i did and will do with other conversions is place the batteries on the sides in the stone guards like the castle conversion kits when they come out. For a 5s setup you could put the 3s pack on the left side and a 2s pack on the right with the motor. You need to do some maths with what the packs weigh against the motor, speedy and servos but i tried to get mine to match left to right and went for a a 45/55 front rear bias. It takes some time but if you want balance that's how i would do it. IF your are not racing though i wouldn't really bother

Speed
 

If you run it with the setup above it will not be drivable. All it will be good for is destroying tires and screwing around in a walmart parking lot when its empty(hahah).
I will have a single speed diff this weekend and will be taking it to the track to see if it helps.

so i think running a 2 speed would be cool but it sounds like it is total overkill. what is a good, drivable, fast setup? i am thinking of just going single speed with the Neu 1512 2050kv on 5s 2600mah. would this be a decent setup? also, what kind of diff can i use for the center diff? do i need to run just a spur gear or would it be ok to acutually run a differential?

inferno single speed
 

i used a inferno diff kit from the 777sp2 and the 46t plastic kyosho spur. all worked well but you need to get the longer front center shaft. i dont remember what the partnumber is but i think it was 110mm i can check when i get home.

perfect. can you let me know on that. i have decide to just run single speed so i knew i would need the longer drive shaft. even if you dont have a part number just the what model its from would help.

also, i dont have my gt2 yet. just ordered thru amain. i am wondering what the pinion shaft size is on the front and rear gear boxes. you know that shaft that comes out of the gearbox and connects to the drive shaft. is it 5mm or 8mm?