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He didn't say anything about a minimum speed I assumed it was any gear. he did say the 3rd gear overdrive is very useful.

I have all the electronic control stuff for the C6 I'll never need if you ever need it you can have it.

 

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I have all the speedometer parts and I don't need them since my speedometer comes off the transfer case.

I bought all the parts I need except the drive shaft from Gearvendor today. they're a lot of things but cheap isn't one. just the adapter to connect the unit to my NP435 is $850 and I have to give them the one for the 205 I have . but it will be nice once it's done.

 

I did it on a 76 F250 4x4 and it works. I had the driveshaft shortened and had a driveshaft shop put a matching yoke on the o/d end. A 5-speed o/d transmission would probably be more work and cost more to install, but it would be better IMO.
My experience with Gearvendors: The Gearvendors company is a joke. The customer service is completely incompetent and they fought me every step of the way once i bought it. I was in another country and purchased a GV unit with the C6 adapter to install when i got home. They assured me SEVERAL TIMES that I could return it if i wasn't happy since it would remain unopened. When I got back and went to install it, I discovered there were missing and incorrect parts and it could not be installed. So I called and wanted to return it. Things got nasty and they decided that now they were not going to accept a return, heck even the owner, Rick Johnson got nasty with me about it. After a few months of back and forth emails they reluctantly sent me an adapter for a NP205 in exchange for the C6 adapter. Now I had a O/D with a slip shaft and they wanted me to bolt it up to the back of a transfer case to a driveshaft that has a slip shaft :/ They argued with me incessantly until I sent them a few dozen emails, phone calls and pictures. A few more arguments later they had me send in my O/D and sent one with a fixed yoke. They did give me a partial refund of $500 after fighting me about who would pay for the shipping because of their incompetence. It was a HUGE pain in the neck and the GV really isn't all its cracked up to be, it shifts hard and has inconsistent shift speeds. I read a lot about them before making the purchase, and I don't remember seeing a single negative remark about them.
It could've all been avoided if they would've simply been decent and honored their word. Now I try and 'share' my experience to any potential Gearvendors customer.
My experience with them was quite the opposite of what I had read; with them was purely negative.

 

I don't like the prices but other than that I'm very happy with the service and the product. I had a few glitches but one of their techs gave me his cell number and told me to call if I needed any help on the weekend. you can't ask more than that.

I can see if you were just used to an auto transmission the shifts might seem a bit harsh. but I've split 2 speed rear axles since I was a kid and it's much easier and smoother than that. I mounted the switch on the gear shift just like a 2 speed rear and it's a breeze.

It may not be for everyone but I'd do it again.

 

They are expensive, similar to what a used 5-spd transmission would cost. The GV on my truck feels like your foot slipped off the clutch pedal when shifting.
It engages at 25 sometimes, and other times around 50mph. They're using a pretty darn accurate hall-effect speed sensor, the shift points should be more consistent.
It will also engage frequently when its cold at startup.
I guess I just expect more for a $3,200 product.

That 75w90 GM oil they specify is expensive. If you call them they'll tell you that Lucas 75w90 syn gear oil is fine to use. Look at the stone-aged manual that comes with your O/D and you'll find it calls for ATF (unless they've recently updated it)
I'm glad you had a good experience with them, I sure didn't.

 

They don't claim they mush into gear , look at it more as an auxiliary box. I use the clutch anytime it would shift hard.

Mine will engage under 20 mph . and never unless I engage it so maybe you have a switch problem.

The 5 spd might be better for anyone that doesn't like unfamiliar things. but I wanted an overdrive and to keep everything original , I can remove it and be bone stock again in an afternoon if I ever want to. and in reality since it will engage in 2nd gear actually have a 7 speed.