RAM 3500 rear axle gear ratio and speed
I bought a 96 Ram 3500 Diesel dually. Soon on the road I discovered that I have great speed - I can easily get to 90 mph - as long as the OD is on. I know that once I the OD is OFF it will go up on RPMs and slow down. It's normal. My problem if that without any load, with OD OFF on the interstate I cannot get it to go beyond 60 mph at 2500 RPMs. If I floor it, the RPMs keep going up but the speed stays at around 60 mph. The transmission is fine, it does not slip and the gears shift when they are supposed to. It has a 4.10 gear ratio. My question is: If I change it to a 3.54, how much more speed am I going to gain with OD OFF.
Is there a little formula? The ratio is about 16% smaller; does that mean that at let's say 2500 RPMs the truck is going to go 16% faster that before at those RPMs.
Any help would be appreciated.