I know you are going to want to stay with tower so you can get the payment plan and if that's the case then you'll want this radio:
http://www3.towerhobbies.com/cgi-bin...&I=LXEDMK&P=ML
I'm sure it's a lot more pricey then what you bought but it is designed for the semi's with all sticks self centering and analog trims. This will be your simplest and easiest choice.
With the radio you have that doesn't have analog trims you will have issues doing certain MFU functions also with the way you have your sticks setup will cause you issues as well since the left stick should be throttle and shifting and right should be steering and horn.