The best bet is to shop at a yard where you can pull the transmission, linkage, torque converter, shift lever & boot, and maybe the drive shaft. Then you get to pull the computer and associated wiring to enable the torque converter lockup solenoid, and starter lockout/enable, and ??? Might need the cross member also to support the tailhousing. This is a lot of work.
I would consider buying a complete truck, swapping what I need and then junking the remainder.
The A4LD can be built to handle the output of a 4.0, and even bone stock haul around an Aero* pulling a trailer full of horseflesh, and even last to 180k doing so. So handling 2.3 output should be no problem if built well.
Unless you really really really like your current vehicle, I would suggest taking your time to find a replacement with an automatic transmission that you like and replace your truck with that.
tom