All pickups are light on the rear. That's where the cargo box is. And the longer the wheelbase, the lighter (proportionally) the rear axle is. A long wheelbase pickup needs an agressive tread (M/S tire) at both ends, and at least 500 pounds of cargo to make it tractable in snow, even if everything else is up to snuff. Sandbags work, if they're loaded just forward of the axle. And you can use the sand for extra traction if you do get stuck.
By all means check for contaminated shoes at both ends. The back brakes will skid if the front ones aren't working, and vice versa. If your shoes are fouled, what works best to clean them is Brakleen; comes in a spray can. Don't be shy with it. If you can't get that, ether (cold-starting fluid) works as well, but is even more expensive. Again, use it liberally. It's cheaper than body work, as Mr. Rod said.
One thing no-one has mentioned is tire pressures. Run them lower than you do in summer. In LT235-R15's on a 1/2-ton I'd have no more than 30 psi if I'm packing no more than 500 lbs. In any radial tire, there should be just a touch of belly in the sidewall where the rubber meets the road whenever traction is an issue. And when you do get stuck, lowering your tire pressures even further is the first thing you should do to get moving if you don't have other traction devices such as chains or sand. Once long ago I was parked on a dry sand beach, and when I went to leave, even with some really gentle clutch work, the drive axle just went straight down. So I dropped the tire pressures to less than 10 psi, and easily drove away. Same thing on an ice-rutted highway: 25 - 30 psi will keep your truck rolling along nicely in a slightly boring manner, while other drivers' knuckles glow white. Washboard logging road? Same-same. Of course, when traction conditions improve, pressures go back to spec as soon as possible to save your tires from damage.
Call me an old nutbar if you want, but when my ducks are all in a row (tires, brakes, suspension, load, traction devices) I am the fastest thing on the road. I have no difficulty pushing a foot of virgin snow at 50 - 60 mph with a LWB 2-wheel drive pickup if visibility's not an issue, and if everything's dialled in just so, controlled four-wheel drifts on a curving mountain road can be fun!
