I have a 96 ram 1500 4x4 with a 5.9 magnum on an automatic.
THe trans when warmed up will not shift up to third & thus at 80kmh, I'm doing 3000 rpm unless I shift her to neutral & give a shot of gas then shift back. Everything goes well after that till next time. THe only time it will shift nicely is if I am going extremely easy on the gas. It doesn't jerk when shifting, nor does it seem to slip. I thought of replacing the valve body or valve body seal kit. I have an auxiliary cooler & I have flushed it out already but to no avail.  

Im not to sure if you have a throttle cable for the tranny since its 96. But if you do mess with that it should help.