Got a 6.2 diseasal... should I put a 700r4 or a Turbo400 behind it?

[Firehound]

Howdy!

I've got a 3/4 ton 85 Burban with a 6.2 in it... It has a turbo 400 behind it with a cracked case. I'm parting out a 1/2 ton 85 burb (with a 350) that has a 700R4 in it...

Here's the quandry: Fuel mileage is a very important consideration. I know the 700r4 will get better mileage with the OD... BUT I've heard lots of nay-sayers telling me that it is a weak transmission to put behind a diesel. Endurance is also an important factor, I dont wanna be rebuilding my tranny every year...

Usage: This rig will be my DD AND my Search and Rescue Rig. Cruisin and 4x4in... when/if I tow, I'll probably only be towing my 3/4 M101 Army trailer (basically an 8' pickup bed with a tarp-top)

In my quest for fuel mileage, how much difference are we talking anyway? 3-5MPG, I may as well keep the heavy duty Turbo400... 10+mpg... I guess I'll go with the 700r4?

Thanks y'all!