I just bought a 97 dodge ram 1500 4x4 with a 5.2 eng.
It runs great , but in ovrdrive at @ 60-65 mph it starts losing speed and is constantly kicking down to keep up.
When i use the overdive off button it does fine, but kills me in gas milage and i'm worried about hurting the transmition.
The truck does have a lift and 37" tires wich i know doesn't help, but does anyone have any suggestions on getting more sustainable power/tourqe/gas milage without hurting the trans?

Change the gears, you probably have 3:55's. With 37 inch tires you need at least 4:56's.