without strength in REVERSE (AW4)

Hi friends, im having problems with my AW4 , driving , shifting, oil level and temp, everything is ok, going out from my garage in reverse is ok, entering my garage or any parking in reverse is ok the problem is when I trie to climb something like the sidewalk in Reverse , it has no strength ,It looks like the reverse only function in flat places,

Any recomendation of what it could be.

My rigs is a 99 XJ sport, front dana 44 and rear gm 9.5 both with 5.38 gears and running 40 inch tires.

Thank you for yor help.!

Does the trans have the correct fluid? That's dex/Merc ATF. NOT the Chrysler stuff. Ever adjusted your TV cable?