First Off. Welcome to this wonderful board! We are a cool bunch of gearheads.
I read your plans about installing a GearVendor Overdrive. I've got one, it is great. But the cost$$$ is somewhat over the top. And the one complaint I have is they generally remove your two driveshafts, and install a single long drive shaft. this is all fine and good, but now when I hit about 70mph, I start having a severe vibration. I believe it is that the long drive shaft is hitting it's "critical speed", or begins opperating within one of its bending frequencies. NOT a good thing. doesn't really bother me as I mostly use the vehicle for towing now days, and never tow close to 70mph.
We can chat more about it.
Steve