I thought decompression braking would be better with the ZF. Are you saying the C6/Gear Vendors is a better option than the ZF in your experience??
I could be mistaken, but I think he was saying that he disliked the lack of compression braking with the C6 so much that he got a ZF5 so he could compression-brake. Certainly, I compression-brake with my ZF5 truck all the time and it works quite well...I can get from freeway speeds to 15 MPH before touching the brake pedal
Personally, I'm a BIG fan of manual transmissions for simplicity and for compression braking. However, if forced to go with a slushbox, I'd shell out the money and build up an E4DOA. The C6 is a strong transmission and can be built to be bulletproof at considerably less cost than an E4DOA, but IMHO the torque converter lockup in the E4DOA is worth the price of admission if you do a lot of highway driving.
Since both trucks are 4x4, the GV unit should either be mounted to the back of the transfer case or replace the carrier bearing, so you should be able to swap it over and run it with the E4DOA and get double-overdrive