Also, I know they're big in the towing world, but +1 for the 6spd

 

wonder if they will sponsor me

 

i would love the double overdrive on the 80e. on the highway if your running a engine with some ***** or with FI you could roll into the throttle a little and just build boost to keep pulling in overoverdrive.

 

Looks like you guys have it figured out already. Yes - you can split each gear but there's no point in doing that if you have a decent amount of power, it will just blow through them too fast. It's best suited for use as a second, or "double", overdrive. I use mine on the freeway and then only if I will be going over 60mph for a while.
I am running 28.9" tires (stock diameter for an OBS C1500) and 4.56:1 gears with a 4L80-E. When I first bought the GV unit I had a 4L60-E and 3:73 gears.
Just keep in mind that it's either on or off and will not shut itself off when the trans changes gear. So, if you hit in in third it will stay on through the shift to fourth and in forth, and remain engaged until the truck decellerates to about 15mph at which point the electronics will disengage it automatically.
There is a new controller available that can engage and disengage the overdrive in coordination with the transmission shifts. This controller took years to develop, they offered it to me but I've not opted to try it for a simple reason. The hydraulic circuit in the overdrive is not pressure modulated. It's full pressure always as long as the input shaft is spinning, no matter what the throttle position. When it engages it hits fairly hard, especially if you hit it at wide open throttle. Since there is no way to modulate its internal line pressure, there's no way to make it engage and disengage mildly that I know of, so it's not ever going to feel like a controlled factory shift like the trans itself.
From a reliability and power-handling standpoint these units are very stong and robust. They do have a limitation in reverse where attention should be paid not to exceed, this goes for downshifting it to engine-brake too which should not be done. Going foward anything is fair game. There is no Gen-III or Gen-IV smallblock powerful enough to hurt one of these things. Let me put it this way - it survived the rear end exploding and locking up which took out the sprag in the 4L60-E. The GV was in between and merely forwarded the carnage to the next component in-line completely undamaged.
GV Overdrives are a compliment to a narrow-ratio transmission like the 4L80-E. Some people complain that the 4L80-E's overall range of 3.30 is too narrow compared to the 4L60-E's overall range of 4.36. The combination of the 4L80-E and the GV is an overall range of 4.24 - and that's about the same as a 4L60-E but with 5 close-ratio gears instead of four that are spread out too far apart.

 

Um, sorry, no. They give discounts to nobody and are as inflexible with pricing as pt.net is with non-sponsor links.
They are also militant about "spare parts" floating amuck. If you buy a different adapter because you change transmissions, for example, they core charge you the full price of another adapter for your old one even though they just melt it down anyway. They're weird but they remain profitable without changing their prices even as times change. This company will be around for a LONG time.