Finally had a few minutes to look at the truck again. I'm sure the problem is with the Bowden cable. It's having the same symptoms as it did several years ago when the adjuster broke. At that time the fix was as simple as a zip tie around the adjuster to get close to the correct length. That doesn't seem to work this time. Going to replace the cable with one from a bad trans I have and change the fluid and filter.
The reason I think it's the cable is I can get up to speed, shift into neutral and back to drive and it will shift, just as it did before. Depending on speed whether it shifts one gear or to high.
I'll update after repairs.

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1971 R600 Mack toterhome (SuperDawg)
99 NU-WA Snowbird 34+2 SE 102 5er
If it's not diesel, it's not in my stable!
53 F100 617.951/auto
95 Dodge 3500 Cummins/5 speed service truck