Before suggesting lifts, a few questions need to be asked. What do you plan on using the truck for? Do you plan on towing anything? What type of loads do you plan on the truck carrying? There are more but lets just start with that.
If the truck is going to be driven on road mainly, with little to no offroad use(or even jst playing in the mud) then a spring lift would be a good choice, and 38's can be installed with just a 6 inch lift and a fair amount of trimming.
But if you want the vehicle to excell offroad then I suggest this opinion, lower CG(center of gravity) and the most articulation you can get the better. The CG for obvious reason as the higher you lift your truck the more unstable it is. And articulation so that you can actually keep your tires on the ground. I have installed tons of lifts, from custom 4 links with rockwells all the way to simple leveling kits.
A 4 inch lift can even be used with 38's if the proper spring combination/trimming is done. a simple 52 inch front spring swap will repositon your front axle and elimate alot of needed trimming. A 1 inch zero rate with a offset will also do the same.
The biggest thing you have going for you is there are alot of straight axle gm's out there , and there are tons of mods for this platform. Good places to gather ideas are like mentioned before
www.coloradok5.com,
www.pirate4x4.com just to name a few.
On my (now gone due to bad accident) m1028 I ran a 5.5 inch suspension, that was composed of a custom 57 inch front pack(built from f150 leafs) with a 1 inch zero rate, 63 inch rear(rear springs off a ifs chevy cant remember the exact year) with a 4 inch shackle flip. I also had some more complicated things on the truck such as full hydro steering. I ran 37's on the street for a very long time with zero rub issues, and 42's offroad with minor rubbing at full stuff. I built this truck for very little (till the cummins swap) and it preformed extremely well, I would drive to local trails to get more wheeling time as my wheeler was trailer only.