If you have it in difflock, and 1 wheel on each axle is slipping / spinning, then your difflock is working fine.
The difflock only locks up the transfer box, sending drive to both axles equally, now the diffs in the axles are not locked, so if 1 wheel on 1 axle slips, the other axle is still being driven so you continue to move, but if 1 wheel on BOTH axles slip................you're stuck!
You'll often hear about "cross-axled" when off-roading, this happens when crossing a ditch or similar at an angle, 1 front wheel & 1 back wheel loose drive because they're near enough off the ground, then you stop.
If you want all 4 wheels to turn no matter what, then you also need lockers in both axle diffs.
Try a higher gear instead of 1st, try 2nd or even 3rd.
The difflock only locks up the transfer box, sending drive to both axles equally, now the diffs in the axles are not locked, so if 1 wheel on 1 axle slips, the other axle is still being driven so you continue to move, but if 1 wheel on BOTH axles slip................you're stuck!
You'll often hear about "cross-axled" when off-roading, this happens when crossing a ditch or similar at an angle, 1 front wheel & 1 back wheel loose drive because they're near enough off the ground, then you stop.
If you want all 4 wheels to turn no matter what, then you also need lockers in both axle diffs.
Try a higher gear instead of 1st, try 2nd or even 3rd.