Looks very familiar engine

. I used similar engine for my swap, it was 6 liter LQ9 from Escalade, but looked exactly the same. I put it to Dodge Raider instead of 2.6 4cyl
Here is my engine before the swap compared to the original
... and when installed...
About the drive by wire systems (DBW) (electronic throttle). Initially I wanted to use all original ECU and DBW, but there were a lot of cases, where DBW reliablity was an issue and calibration went wrong. Also with DBW you are not controling the throttle butterfly directly, but with pedal you are giving your request to ECU and ECU is deciding how much and how fast the throttle would be applied.
So I wanted to get rid of the DBW system and went for a cable and bought a new throttle body from Camaro. Then there was another problem. Eventually ECU and wiring loom was different for DBW and cable throttle, so I went for Megasquirt and EDIS. The result is very good 386hp and 397 lbft.
About the transmission
I guess the tranny you got is 4L60E or 4L65E, which is probably not the best tranny for offroading...
I used manual NV4500, but not sure was it right decision, maybe auto woud have been better...
I saw your engine has cast iron block, so if it is 5.3 liter, then it should be LM7, if it is 6.0, then LQ4 or LQ9
What axles and tires would you be using? Actually I'm planning to change the axles and one option would be LH61 axles with lockers. Does anyone know how much power and tire they would stand?