Hi Jim,
</font><font color="blue" class="small">( So even with the diff lock pushed in I only had the traction of two wheels... )</font>
Just to clarify a bit. At that time, you only had one wheel which could provide any real "push", and that was the rear wheel that was stuck in the hole. Since it had snow and ice around it, it had little ability to help get you out. The front wheel that was on the ground had just about no ability to push because the opposite front wheel was not on the ground. Without a locking differential up front, the wheel with the least traction gets all the power, and that was the one in the air spinning. The one on the ground was no help at all.
Many years ago someone posted something along the lines of this:
4WD tractor in 2WD mode = 1 wheel drive (one rear).
4WD tractor in 4WD mode = 2 wheel drive (one rear, one front)
4WD tractor in 4WD mode with diff. lock = 3 wheel drive (2 rear, one front)
There was an additional comment about having a loader and/or backhoe in order to "really" have the effect of 4WD.
Any vehicle can get stuck. That's why serious off-roaders have winches mounted on their vehicles to help pull 'em out when all else fails.
In your case I would consider a good set of chains as a first step.
Good Luck,
~Rick