Another gear...

[piersbc]

My truck is a daily driver hardly ever tow anything more than a couple waverunners....and at 70mph I'm turning 2100 rpm. Does anyone make an overdrive unit that would get me into the 1850 rpm range at 70 mph?

[More Power]

http://www.gearvendors.com/

Jim

[Hubert]

Or usgear.com

[chris_maxwell]

I love my Gear Vender, expensive up front but heavy duty. They also have great customer support!

[moondoggie]

Good Day!

"...at 70mph I'm turning 2100 rpm." Actually, it calculates out ~ 2000 rpm @ 70 mph with your gears & tires.* So, you're already better off than you thought.

A Gear Vendors Aux. OD (0.78 ratio) like mine would get you to ~ 1565 rpm @ 70 mph, which is almost too slow.

What's your issue?
Noise? Yep, your truck would be much quieter at the lower rpms. If Scotty beamed you into my truck while I'm going 70 mph, you wouldn't know it's a diesel.
mpg? LLLLOOOONNNNGGGG payback. If you paid $2700 for a GV, get 18 mpg now, figure to get 20 mpg with the GV, & diesel costs $2.60/gallon, it'd take ~ 187K miles to pay for it. (I have a spreadsheet that calculates this for me.) Plus, you're already running just about where you want to be for best mpg. According to the very recent DP article, best mpg is right near peak torque rpm, which is 1800 for our trucks. Soooooo, you might actually not gain much of anything by dropping your rpms this much.
Blessings!

* rpm = (mph) X (1 hour/60 minutes) x (63,360 inches/mile) / (tire dia in inches x pi) X (driveshaft rev/tire rev [axle ratio]) X (0.75 engine rev/driveshaft rev [AT OD ratio])