There is a FSM for the JR403 here http://daemon4x4.org/portal/downloads.php?dcid=5&p=2 IIRC, it has extensive diagnostics. Also, I remember reading somewhere here that sometimes the TCM gets lost and need to be reset. It then goes through a learning and calibration process that takes some time/miles of driving.
Pull the ATCU fuse on the left side of the fuse panel in the cab (ATCU something or other, there is another in the group to the right, but that's not it) pull that, count to 10' put it back.
Climb into the driver's seat, turn the key to "run" (note: for this do not start the truck) with the
Trans still in "park" push the accelerator slowly to the floor, then release, repeat 2 or three times, twist key to off.
Make sure the "throttle advance is adjusted all the way off.
The last bit with the foot feed sets the range of the "TPS" so that the trans will not have to relearn that hole driving.
Your issue is notnwhatnI was having that caused me to reset mine.
Got the directions from BobPR, he's on the opposite end of the Pacific from me.