Not too difficult. Just look through any of the swaps putting these into Jeeps, to get some ideas.
The 6.0 is a nice motor as a starting point. They take well to upgrades. 243 heads will bump the compression nicely, those with a good cam will net you 425-450hp or so. Switching to rectangle port heads or aftermarket cathedral ports even more.
IIRC, the 4L60 you have is a 27 spline output and the 4L80 is a 32 spline. I'd just grab the t-case also while you are getting the engine and trans.
Its your truck, you know best if its worth the upgrade.
Any motor swap, you neeed to just go down the list and look at the things you need to do to make the swap:
Engine & transmission mounts (you can get plates to adapt your existing frame mounts to the 6.0, but likely need a new/reclocated trans mount crossmember)
Driveline adapters (shouldn't need any, but likely need driveshaft modifications)
Fuel system: Probably OK with the existing in tank pump, you'll need to make 56-58psi at the rail.
Cooling system: You can get hoses/adapters to use your existing radiator if its in OK shape.
Exhaust: You'll need to have it modifed to meet up with the new headers/manifolds
Wiring: Probably the biggest thing, you need to have the harness modified to your needs, and the computer setup correctly.
Gauges: NO idea how the stock chevy gauges/cluster are, the 6.0 is all metric senders, you might be able to adapter the old gauges, probably best to make a custom clusters with aftermarket gauges. The tach signal is funny (need an external pull up resistor and gives a 4 cyl output).