Ok I need some input. I have a 97 4x4 dually, 3.5 gears, with 235/85/16 size tires on. I replaced my speedometer gear from a 31 to a 29 tooth, and my speedometer is still off.
With the 31 gear the speedometer was showing 75 mph, when I was actually doing 67mph.
Now with the 29 gear when I'm at 75 mph on the speedometer I'm really going 70 mph. (This is measured with a GPS).
Odometer was 2/10 off but now is 1/10.
Anyone have recommendations?
Think I should go with a 27 gear?

 

Im having the same problem. I would like to know this too.
I called dodge and they were the ones who said I needed a 30 tooth, so I ordered it. I installed it and the speedo is still off.