To give you a more complete answer: Up to about '06 the trucks/vans from GM had Gen3 engines with 24x crank sensors and the PCM (powertrain control module) had two big flat plugs. Red & Blue for the earlier ones, Green & Blue for the later ones. These PCM's run both the engine and the transmission out of the one box. This system could have a cable throttle or an electronic throttle and always ran on all 8 cylinders. These are the better system for an OBS. The '01-02 PCMs with Red and Blue plugs with a cable throttle would work the best with your gauge cluster and cable throttle system. The 6.0L HD engine from this year range is called an LQ4.
'07+ Gen4 engines and transmissions can optionally have the 6 speed, but that's about the only improvement (and I think the 4L80 is better personally). They use an electric throttle, have two different computer boxes with one each for the engine and trans. 58x crank sensor and wheel is pressed onto the crank so you gotta take the whole engine apart to use a gen3 computer on a gen4 engine. Ligenfielder or somebody makes an adapter box for like $300 don't know if they're any good. If you want to use a gen4 engine, find a 6.0L van from '07-'09 because they mostly (all?) came with a 4L80, so they'll have an engine and trans computer (tcm) that can run your current trans. Dumb thing about Gen4 is they all use a BCM (body control module) to run all sorts of crap in the cab (part of the dash even I think) so making it work in your truck might be harder to do.
I'd keep your NP241/NP243/BW4401 t-case in your truck, it's better than what the newer trucks have.
Best possible combo would be a gen3 LQ4 with an 0411 PCM and a 4L80e with an NP241 or BW4401 with a stick on the floor. Or go to an ford NP205 if you want a better T-case. Good luck!