What could cause a CAT 938G transmission to stay in forward even when the shifter is in neutral or reverse?

[Mc Wyndell]

CAT 938G intermittently stays stuck in forward even when shifted to neutral or reverse. No ET codes, and it shifts perfectly when the issue disappears. Moving the steering column or parking brake handle sometimes changes the fault, so I'm leaning toward a wiring or connection issue. Already replaced the park brake switch with no luck.