I had a 2wd sierra with the 24v cossy lump in it.
I found that the type9 just couldn't cope with the power i put 2 type 9 boxes in the car within a few months,

I then dexided to put a 2wd mt75 gearbox in instead as theese are meant to be a much stronger box. I only did about 200 miles in the car with the mt75 box in then the engine let go , so i dont know if the box was any stronger,
But i can say the gear ratios in the type 9 were a lot better than the mt75.

I'm sure the ratios on the 2wd boxes and the 4x4s are the same but i have been told the 4x4 type 9 like what you have, has stronger internals than a 2wd xr4i box.
so if you find this to be true i would definateley recommend the 4x4 type9.