My C6 and 3000 stall is killing my highway cruising, trans tends to get to 220 pretty easily on a hot day only going about 20 miles on the highway. I've been looking into an OD for the trans as well and would like to hear what ppl have to say.
Your other options that I've found is an adapter plate to attach a 700r4 or a AOD to the trans. Adapter start around 450$. This is great as I have lots of experience with 700r4s on the past and they can handle 600-700hp and offer a lockup converter! That's going to be the single most important part of an OD trans swap.
The GV unit is nice but also has its drawbacks. Since the C6 doesn't allow for a lockup converter ur basically just stock with an extra gear, which will lower rpms but increase leverage so still expect your converter stall to be normal.
Basically I can cruise at 3k at 55-60mph since my stall is 3K, the GV unit will drop rpms but since I'm still under the stall of my converter and the added leverage of the taller gear means my converter will still likely stall at 3k at a slightly higher cruising speed. Only way to really lower cruising rpms is a lockup converter which also dramatically decreases trans temps. So your stuck with the AOD, 700r4, 4L60e, 4L80e, or the E40D or the other posted before.
521 BBF 10.8:1 FAST EZ EFI 2.0
2004R GM OD Trans swap, NX NOS kit