I couldn’t get my truck to go into 4x4 at all and so i replaced my shift motor, now i can get it into 4low but only when i hit the transfer case with a wrench while someone else shifts the switch in and out of 4x4
I also recently installed the manual locking hubs to ditch the PVH system but still no luck

 

PVH system needed to changed to manual but wouldn't effect transfer case shifting

4low requires foot on the brake and
transmission in Neutral(not Park)
or
clutch pedal down all the way

Reads like the new shift motor has bad brushes, common issue on old shift motors, tapping on the motor or case gets it working temporarily
See if seller will warranty it, some don't because its an electrical part

Try this test first
Take the shift motor off the transfer case
Plug it in to harness
Shift to 4high and then 4low and then back to 2WD, do it a few times to see if shift motor works without issues
If it stops working tap on it, and see if it starts to work again

If shift motor sticks in 4low position while off the transfer case then it may be out of adjustment
There a physical limiter/stop on the gear drive inside the shift motor, so it can't turn past 2WD or 4low
If it was mis-adjusted then it may be turning too far in 4low, this causes a high torque on the motor part, so in essence, it locks the motor from turning the other way, out of 4low, unless you tap on it while motor is activated to release the torque

No, shift motor does not need to be grounded to transfer case, just FYI for testing