Has anyone changed their rear-end gear ratio? I've a 3.73 duramx van setup. These are the RPM's I've been seeing:
55 mph 1723 RPM
60 mph 1885 RPM
65 mph 2055 RPM

With 3:42's 60 mph would equate to 1700 RPM
3:23's 60 mph to 1600 RPM

How would the speedometer and odometer be calibrated if the gears were changed?

Can you recommend a source for purchasing the gears? Any idea on labor for installation? It is a locking-differential rear.

Thanks!

I'm toying with this as well.
A $600 cost to swap ratios factoring an improvement in mileage from 18 to 20 MPG with fuel at $3.50 will take 31579 miles to recover cost. At a consumption of 1 gallon a day, the swap will be paid off in 4.33 years.

I believe every 10% rise in RPM over 1700RPM is equal to a 10% reduction in MPG. Thats what I've seen.

It gets interesting when you factor in the 6 speed conversion with .61 final drive(5 speed is .71). That gets you to 1609RPM at 70MPH. Ideal RPM at my desired cruise speed. These trucks are geared to cruise at 55MPH.

One guy on here has done both but good luck getting him to talk about it.

I get about the same mileage at 55 mph as I do at 70 mph. It just doesn't seem to matter much. Don't expect miracles by changing the rear gears. If you do more driving in the city (stop and go), you may see a decrease in mileage because of the tall gears. Acceleration will not be as brisk and may require more throttle.

Jake

Thats what I see with my DMAX keeping constant RPM over 200 mile distance. Its true that the gear change will work best for someone driving mostly on the interstate.

My truck has 285 on it that came with the truck and it has no trouble getting going. Many others have no problem towing at max capacity with oversized tires or higher gears. I like the ratio I have but want 245 tires and changing to 3.42 will put me back to the same.

245 w/ 3.73 & .71 = 68.52MPH @ 2K RPM or 2043RPM @ 70MPH
245 w/ 3.73 & .61 = 79.76MPH @ 2K RPM or 1755RPM @ 70MPH
245 w/ 3.42 & .71 = 74.74MPH @ 2K RPM or 1873RPM @ 70MPH
245 w/ 3.42 & .61 = 86.10MPH @ 2K RPM or 1609RPM @ 70MPH

285 w/ 3.73 & .71 = 73.69MPH @ 2K RPM or 1900RPM @ 70MPH
285 w/ 3.73 & .61 = 85.77MPH @ 2K RPM or 1632RPM @ 70MPH
285 w/ 3.42 & .71 = 80.37MPH @ 2K RPM or 1742RPM @ 70MPH
285 w/ 3.42 & .61 = 93.55MPH @ 2K RPM or 1496RPM @ 70MPH

it was mentioned before, but how much do the rpms drop in the newer vans that have the new style(6l80e?) transmission? and are they rated with a better mpg figure? or maybe the government doesnt rate them...

it was mentioned before, but how much do the rpms drop in the newer vans that have the new style(6l80e?) transmission? and are they rated with a better mpg figure? or maybe the government doesnt rate them...

They have a double over drive 6l90 and 3.42 gears.