Auto trans shift lever adjust

[Mertz]

I have a 72 Chevy 3/4 ton with 350/350. The transmission was just rebuilt by a very reliable person. I am having problems with the shift lever on the column staying in place. I tried to make some adjustments but it will be in reverse and show N and drive shows low. If I move it up in drive I can get it to hold there. There was a time when it won't hold there either. I check my manual but I am still not clear on what to do to fix it.

Any help would be greatly appreciated.