Re: Transmission Downshifting Issue...
There is a TSB for this. The 05-06 GC's had an issue with water getting into the tranny which can cause the issue your having. It is actually a recall: http://wkjeeps.com/recalls/wk_recall.htm#E1305
like you were told. There is also a software update to resolve issues with the transmission. http://wkjeeps.com/tsb/tsb_wk_2100805.pdf
Print those out and bring it to the dealership. They usually have no idea when you tell them.
2010 Jeep Grand Cherokee Laredo X, 5.7L HEMI, MYGIG 730 Nav, LED interior/License Plate/Reverse bulbs, Mopar CAI w/Amsoil Synthetic Filter, Gibson 3'' Catback Exhaust, SRT8 Front and Rear Swaybars, BT Black anodized PCV Catch Can, Diablosport Predator Tuned