I had one of these in a Volvo 2001 with a Detroit 60.
I regret getting rid of this one only because of the engine which was pre EGR.
I had similar problems and eventually it led to having to rebuild the shift tower. My truck had the square box on the dash and the shift tower on the side of the seat had the shifter with the buttons on the side of the grip to manually shift the tranny.
That rebuild cost me over 3000.00 not counting the batteries I had to put in.
It seems that every time we bring these trucks in for service the first thing the dealer wants to do is install new batteries.
I will also point out that on my truck the slave cylinder on the clutch came in the vertical position and was not robust at all.
When I did a clutch job on the truck which was prompted by that slave cylinder falling right off one day....the mechanic put the new slave cylinder on that was bigger and it was installed horizontally. Bigger bolts (the old ones snapped off easily) came with the upgrade kit.
This issue always starts with a few codes, then you will experience nothing for a while, then the darn thing will start beeping to beat the band.
You can un hook the power to the ECM and Tranny ECM and it will go for a while.
But eventually it will just quit shifting all together.