Not sure if these things have grade logic or not. Or whatever Ford calls it. Your first order of business if the car is doing this is to keep OD off going up hills. If the car doesn't have the capacity to realize its on a hill it'll stay in a too low gear and lug itself up the hills which is actually really bad to do in OD.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.