i have a 2000 3500 auto 2 wheel drive this is my first diesel is it normal for the trans to shift into overdrive at 2000 rpms around 45 mph it shifts kinda hard too, the other gears shift fine not as hard as overdrive just wondering if this was normal the motor has 145000 on it i dont know if the trans was rebuilt or not, the trans fluid looks new.

 

Depends what was done to the transmission. If it is like mine with a shift kit and the line pressure turned up to the max, then Yes it will. when mine goes into OD it will put you in the back seat.