How serious do you want to get?

For starters I would suggest installing OME 912 coils to lift 30mm (1.25"), adjusting the ride height in front to match via torsion bar adjustment. This will give you plenty of room for 265/75 tires, and the ride and load carrying will be improved also. You can always go higher via coil spacer later if desired.

If you are getting serious at all, I also recommend tie rod protection (they are the first thing to break) and rocker panel protection ("sliders"). After that you could consider manual hubs (which BTW can gain you ~1 mpg since the front drivetrain no longer has to turn all the time) and shock upgrades.

Your best resource for aftermarket upgrades is Independent4x in Richmond...you near there? They are about the only full-service Isuzu aftermarket shop out there. Calmini has a few products also.