I have a 2006 Freightliner business class m2. It has a cat C7 engine. The rear Axel has a 3:90 ratio. The problem I am having is the truck does 80-85kph (50 mph) at 2200 rpm. The truck can only do 2500 rpm max. The Engine is just screaming the whole time. I was told by freightliner if the rear diff ratio was changed to a 3:70 I would be able to get 100 kph (60mph) at around 2000rpm. However the Rear diff company is saying the 3:70 rear diff ratio will only get me about 7% more speed. Has anyone ever done this before? Any advice would help.
