Not sure why, but when we had some bad snow this winter I took my ebrake off and coasted backwords down my driveway. When I went to move foreward it was locked. Reverse was no problem when I tried a second time. Ended up getting a bucked of warm water and splashed them. Melted and was fine. My neighbors laughed at me for driving the GTO in the snow anyway, then alittle more for stalling when the car wouldn't go foreward. I love my Potenza 960AS. They never let me down.
I'm sure yours isn't snow related, but maybe something mechanical will alow it to go reverse is something fails?
2003 Corvette Z06 - MGW shifter, Corsa X pipe, Corsa Xtreme exhaust, Texas Speed long tubes w/o cats, PowerStop rotors/pads, Conti DWS tires, C6Z51 F&R sways, C5R headlights, tuned
04 GTO - sold