For what you plan to do I would suggest a 14bff and dana44 combo, if your going to do it you'll find that a 14bff will not cost you a whole lot more than a 12b and it'll handle anything you can throw at it. Everyone will probably tell ya' to go the 14bff/d60 route which would be nice but for on road and the occassional mud (not nearly as hard on drivetrain compared to rocks) I know you'll be fine with the 14/44 combo.
As far as the swap goes it is pretty involved...
For starters you might want to go with a kit from ORU to help get you started...
http://www.offroadunlimited.com/ProductCart/PC/viewCat_P.asp?idCategory=181
Next you will have to look into what you want to do to your axles. If you buy them already rebuilt/beefed up (whatever you choose) then your set. If not then plan on buying a kit to rebuild them and look into a set of gears and if your serious about the mud a locker in the rear would be one of the best upgrades you could do....
Randy's Ring and Pinion sells master install kits that include everything you would need to rebuild your axles w/ the correct gears.
Clicky Clicky
Just choose the kit that has the new ring/pinion ratio you need for your new meats.
GM 14b
D44
As far as gearing goes a good calculator like the one on
www.4lo.com will help you out with the choice. For example assuming you have your transfer case in high (1:1) and you have a 4l60 (?) you would have something like this...
Tire Diameter: 38"
Diff. Ratio: 4.88
RPM: 1963.3
Transmission Ratio: .7 <--in OD (4th gear) as and example
Transfer Case Ratio: 1:1 <---in high it's 1:1
MPH: 65
So if you went with something like 4.88's in your axles you would be able to keep the rpm's at a little over 2,000 (factored in real world friction) and still be able to run 65mph. Use the calculator though to figure out what you want to do, since it's mostly going to be street driven I would concentrate on that since you can keep it in a lower gear and put the transfer case in low when off road.
www.4lo.com/calc/gearratio.htm
Now I haven't done any SAS yet but from what I know you would also have to keep the Transfer Case in mind. Where your current drop is and where the new one would need to be with the new axles (if the ring/pinion is off-centered or if it's centered, etc.) so do some research and you should be able to find what you need.
Keep High Angle Driveline in mind, he'll take care of you when it comes time to get the new axles cut.
http://www.highangledriveline.com/
Ok, finally comes the rims and tires. Since you will be running mostly on road with the occassional off road blip through the mud something like boggers are out of the question. Something like a TSL Radial or TSL SX would suit your needs, relatively long life on road yet it'll get you through the goopey stuff. If you have the $$$ you will probably want to get a set of on road tires and a set of off road tires. Something like Trxus Mud Terrains for the street (you'll still have the size and agressive look but be able to run quitely down the road for many miles) and a set of boggers for off road. Search on here and you'll get a good idea of what each tire is good for.
http://www.intercotire.com/site.php
Ok to wrap up this rediculously long post is the suspension. Now most of the guys on here are into the 4"-6" range because it allows you to fit basically whatever tires you want (mild to wild with the sawzall trimming) and it is the flexiest thing you'll ever see. For someone like me and what sounds like you I run a 9" Superlift (all spring, no blocks, don't ever go w/ blocks) and it suits my needs. Not exactly flexy but for mud/sand that doesn't matter and it allows me to run 38.5" Mickey Thompson Baja Claws with no problem.
www.superlift.com
Hope that helps. Let us know if you have any other questions.
-Avery
