Replace the boot. Yours is how old? I can imagine that under harsh conditions (heat and cold) that the rubber will lose elasticity and become harder to manipulate. My old boot was in good condition until I tried to move in when it was too cold. My new boots are fresh and moist and are very flexible even in the cold, but they're less than 2 months old.
89 YJ, 4.2L MC2100 carb conversion, nutter bypass, AX-15 tranny conversion, rhino lined tub, 33" Treadwright Mud, 2.5" RC lift, 4.10 gears, Aussie locker front and back