We just put a transgo shift kit in my friend's 2007 5.9 48re truck along with a goerend trans. pan. Now it shuttle shifts when under light throttle. Once you hit 30mph, the truck shifts into 3rd, and immediately SLAMS back into 2nd and stays until you put more throttle into it. Under moderate or heavy throttle, it will shift fine. Its only light throttle driving i.e. going through a neighborhood doing 25-30mph. Need some guidance on how to fix this. Truck has 45,000 miles on it. Thanks in advance.