Hello Drivers
I'm having a problem with my 1998 F73 4Trak.

Recently had clutch changed and had mechanic take a look at transmission that had a couple problems (1st gear and 2nd would pop out going downhill. Had strange rattle when clutch depressed...)
Mechanic did an awful job and created more problems than sorted. Messed with the 5th gear/ Reverse bolt "thing" (cannot remember the name of that mechanism) in the transfer case and it just fell off from the case one day. I stopped going to that mechanic.
Had another mechanic "fabricate" another one.

After that, my transmission was grinding, specially when engaging reverse and 5th, but it would engage eventually.
I have to mention that I was never able to engage 4H or 4L on the car (lock hubs were faulty but also transfer and probably differential). But it drove fine before that mechanic episode, on 2H.
I put a spacer on my clutch cable behind the firewall, engine compartment side, to allow smoother shifting since my cable had no adjustment left on the grooves (even though I had the whole clutch system replaced, cable and all. Was suspecting a faulty Spigot shaft bearing. I think the mechanic might have used a spigot shaft bearing from another make/model vehicule). Spacer gave me a much smoother clutch operation and gear shifting.

Now, since a few weeks, when traveling long distances, at moderate or high speed (80kmh, 100kmh or above), my Transfer Lever (2H / N / 4L - Have 4H on button) pops out from 2H to N with a loud grind.
I am able to reengage 2H and drive if I hold the lever in place for a few seconds then let go.
But it will pop out again. And will reengage like described. And will pop out again....
????????

I am not very knowledgeable nor equipped mechanic wise. But.... would appreciate any advice or insight on that problem. To know what to look for, or what to tell a mechanic. Or eventually fix myself.
There. Hope I have provided enough details and context.
All input appreciated.

Thanks.