[68Timber]

I have the 6.2/TH400 in my military blazer. These trucks have 3.08 gears. My speedo cable needs to be replaced so I don't know my mpg. But other CUCV owners regularly report 20+ mpg hwy. I really doubt that is at 70 mph though.

Here's my take on it. The TH400 is hell built for stout even in stock configuration and if you choose to rebuild that transmission, it'll likely be the last time its rebuilt while you own it. It will also be the least expensive route. The TH700R4 earned a bad reputation from the first and second gen models in 1982 through 1986 model trucks. But they can be rebuilt to hold insane power now - all bugs have been discovered and remedied. The burden is yours to find a transmission guy that can do it right. They've been around so long most any trans guy worth a crap knows how to do this.

I'd rather have the overdrive. It's not going to deliver 3-5 mpg, maybe 1-3. But you'll be able to cruise at 70 or 75 and still get 20+ mpg.