98 GMC 2500 4x4 5.7 vortec

For some strange reason this truck will stall from time to time. It only does it in Reverse and has become more frequent since I began plowing snow and if I'm backdragging with the front blade it'll do it from time to time. I'm wondering if this could also be connected to the sometimes surging idle that it contracts at stoplights and such? It generally idles at 600rpm but at stoplights it'll quickly jump to 8 or 900 every 3-4 seconds and immediately drop back down. Neither of these are really a big deal but are a bit annoying.

Also, why is it that the distance between the front tires is further than the distance between the back tires? I recently got a new set of snow tires and realized that it looked a bit odd and was tracking differently in the snow. The distance from inside sidewall is 58" at the back and 62" at the front...??? I've never noticed another truck like this

 

That stalling sounds like a faulty TPS.