Truck is an '83 F250, 351W, C6, NP205?, 4x4. We got some serious snow this past week and my driveway is a very long uphill climb currently covered in 18"+ of snow. My truck has been negotiating this just fine but I've noticed the last few days when I turn put it in reverse I get a loud squeally, whirring sound front right in front of the cab.

Ever since the squeal started the truck has been running funny, wanting to stall and hesitating when accelerating. Tonight when I went to reverse I got very loud squealing and reverse doesn't work at all, in 2wd or 4wd.

What could be the problem?

 

When you put it in reverse, the engine idle does not drop at all, like it's not in gear?

 

Yes, that's exactly what it does.