Hey guys and girls; I just bought a 93 D250 with the Cummins and a A518 auto transmission. Knowing a little about transmissions, I'am aware that the torque converter in the A518 does not have lockup. Is anyone aware of any tricks to decrease engine rpm at highway speeds and/or being able to get full use of all that cummins power. Without lockup or some form of direct drive not all that engine power can be utilized. I'am considering converting to a manual(such as a NV2500). Does anyone have info on what is needed to do this conversion, and has anyone done this themselves? Thanks in advance for any help you can provide.