The Chevy springs wont help with the bumps anymore than teh stock springs do, probably not the coils either unless the stock springs are already shot. If teh stock springs are sagging, then you can either rebuild teh spring pack usuing some full size springs(iI like useing longer leaves from the 56" chevy springs), or the coils. You need some better quality shocks, Monroe sensitracs work well but run about $50+, I run Procomp in mine and they ride nice enough but my rig weighs about 1k over yours so they might be too rough for your wants.

The main thing you can do to smooth out logging roads is run lower air and speed. I run my 33's at about 12-15 psi for the logging roads, and clip along at about 25-30mph, fast enough to smooth out the bumps, yet slow enough to be in control and not stir up too much dust. You can run the roads faster than 30 with my set-up, I have gone faster when conditions allow for it, but at those speeds stopping takes a lot more room and time, and I am usually never in that much of a hurry.

An AT tire will be smoother than an MT, the AT's sidewalls aren't as stiff as MT's, so they flex more absorbing more of the bumps.