The electronic shift T/C's were just coming in when I retired, got some training on them but not a lot of hands on.
Have to ask , can you get the T/C to make any shifts ? 4X4 ? High range to low? Or is it just the shift 2wd to neutral that is the issue. Could be the little push button is shot.
If I remember correctly the , shift required , an input from the brake light switch or the park brake switch, to make sure the truck wouldn't roll away.
Have you checked all the fuses ? Does the park brake light on the dash come on when the pedal is pushed?
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.