I've got a '90 Suburban, 454, 3.73 gears and tow a 26 ft travel trailer (probably about 7,500 lbs). Even installed a GearVendor overdrive.

Pretty much use it only for towing now days, and get about 9 miles/gallon. Solo get about 13 mpg. Everything except the transmission overdrive and Aluminum radiator is stock.

Hey Stevie, how is the GV overdrive working out? I have been looking at those. What is your RPM at 60 mph with the overdrive on. Is the overdrive automatic or do you switch it on. Thanks

Gregory,

Honestly, for me it’s been great. But there are several factors that you must consider before you buy: Cost, age of vehicle, cost, your type of driving, how many speeds the vehicle already has, cost, and what type of vehicle you have. Oh, and cost.
I don’t know what the highway speed RPM is. But it definitely lowers it, and makes the vehicle a little quieter.
Let me explain a few other things. This is not your everyday add-on, it is expensive. I would only suggest it for a vehicle that doesn’t have an existing over-drive. My Suburban only had the 3-speed automatic. I’ll repeat that, if you have an overdrive, don’t buy this product. Give your money to a worthy charity instead. Because having it installed can also create other problems (additional maintenance to worry about, and a possible drive-train issue I’ll discuss later).
Does it get me up a hill faster? Maybe 1 out of 10 hills I may find a “split” gear to be better than the stock gears. Faster? No. But I do like the overdrive feature, as it lowers rpm and noise. And I am a mechanical engineer, and enjoy being able to control an automatic transmission a little more. Does it go into overdrive automatically? Yes. You can also do it manually with a foot switch…very cool. But is it worth $2700 for having a cool switch on the floor? Only if you have a 3 speed transmission.
Cons.. and these are important. My Suburban came with a two-piece drive shaft, and when the GV was installed they replaced it with a one piece drive shaft that is pretty long. I now get a nasty vibration at speeds above 70mph, which is because the shaft is hitting a natural frequency (“critical speed”). It bugs me, but not much I can do about it, nor do I want to bother. As I only use the truck to tow a trailer, so rarely am I over 65mph anyway. I still have the original shafts, but the center bearing would need to be moved aft about a foot to balance everything out. Not worth it to me. Also, one more thing to maintain, although relatively easy. Downshifting takes a bit of practice as you need to press on the accelerator to rev-up the engine a bit (if you don’t you will feel a heck of a jolt). Final “con”… I think the cost is too much.
Pros.. It is cool, and a little fun. And it does work flawlessly. I’ve had mine for about 10 years, maybe 70,000 miles, and it still works great.
Any other questions?
Steve

Ya know Stevie, your post makes me really glad that I have a stock overdrive tranny ;)

Gents... my dream truck is a Duramax with the 6 speed tranny. ...Someday.