I installed one in my Blazer over a decade ago. Love it. I have a mild lift, 4.10 gears and 35" tires. Had the rear driveshaft built with a CV joint at the gear vendors end with a Cadillac series 300 slip yoke to conserve length. I tow a 6,000+ lbs boat and loaded car trailer on occasion. No vibration issues.
The Gear Vendor unit allows you to split all forward gears so you get 1st, 1st OD, 2nd, 2nd OD, 3rd, 3rd OD, 4th, and 4th OD. This makes towing up mountain passes easy because you can always find your engine's RPM sweet spot to maximize torque output.
The brain has two settings controlled by a toggle switch, AUTO and MANUAL. In Auto mode, the unit will automatically engage and disengage at preset speeds. This is nice if you have an automatic transmission. In MANUAL mode, you use a floor switch (high beam switch) to turn it on and off at any time. When I first installed my unit I had an auto tranny, and used both the AUTO and MANUAL modes. But mainly the MANUAL mode. I now have a manual transmission so I can only use the MANUAL mode. I also had to move the floor switch to a pull switch mounted on my shift lever since I don't have three feet
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I found my unit used in a junk yard with unknown miles on it. Gear Vendors sent me a users/technical manual for a small fee, which was a great help. I put another 150,000 miles on it with only changing the fluid at regular intervals. When it finally started showing signs of wear (slight vibration, and harder engagements, along with more metal sludge in the bottom of the fluid reservoir), I decided to pull it and send it to Gear Vendors for a rebuild. When I contacted Gear Vendors and told them the serial number of my unit, they told me it was one of their very first versions they sold, and that many upgrades have been made over the years. It was like almost 20 years old. They still offered me the same rebuild service that they offer everyone else that bought one new, which consisted of me getting a fresh, fully upgraded unit off their shelf with a core exchange of my old school unit. They shipped me a new unit the same day, and I shipped them my unit back in their special crate with return shipping pre-paid. At the end of the day it cost me just under $1000 to get a brand new replacement unit. That is pretty darn good considering I paid $100 for the junk yard unit, and was able to get 15 years of reliable service out of it. I suspect my new unit will last longer than 20 years with the design improvements, and me being able to provide proper maintenance from the get go.