welcome to the world of isuzus. First off never shift into 4wd at highway speeds.It doesn't even make sense to use 4wd at 50 let alone shift into it at 50. this is not italian sportscar AWD this is 4wd that operates differently (simpler mechanism) yet less room for error. I am not a real expert on the sotf system but I have a 98 and I think they use an axle disconnect and automatic hubs. The disconnect is solenoid activated via engine vacuum. Auto hubs are torque activated.

CHRIS
98 Amigo, 92 Pup

need a pickup 1st gen fuel level sender