I would try all the possible permutations of the dsc and dtc active and inactive and possibly manual mode see if anything works.
The situation ur describing is probably ur tread life or lack thereof. If u have winters on, ur nannies should complement ur steep hill Climb (if operated as per the manual). However if Ur close to replacement time, the only reason I can think of why ur able to sucessfully climb in r, is due to the rear biased x drive. (ergo if ur stuck in a rwd car, reverse will be a better option than d, while a fwd car forward is the better option).
BMW and Mercedes Build Beta Products!
Lexus build Release Candidate Products!
Why does this matter?
CAUSE EVERY TIME someone says Lexus has better build quality, one should consider what Toyota their Lexus Engine and chassis platform comes out of and how long that part has been tested in the real world!