Also check the 2 drive belts, long one from engine to transmission and short one on drive pulley, if you haven't changed them in a long time they are worn and stretched.
To change them loosen bolts on outside frame so toy can move pulleys enough to slip belts on, otherwise it's almost impossible to slip belts between frame and the two pulleys.
I have a 2013 Bronco with same stup.
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Look at transmission area there are 2 bolts you can loosen one on each side si you can move pulleys enough to slip belts on.