I know that in 1.2.3 was fixed a trick with "quick stop" - when you switch on full speed to reverse gear.
But now, even on a small hill, the tank slides down. In this case speed indicator shows 0 km/h but you can not switch to first gear for stop tank.
And if you looks down the hill - you can't set reverse gear.
I think that switch 0=>-1 or 0=>+1 must be allowed in speed interval, say, [-2...+2] km/h
Such "gear jam" occurred not only in mountains.
If you run gun in the house or into another tank, you can't drive back.
p.s.
Another way for "quick stop" now discovered - when you press the "c". And it looks very unrealistic - momentary stop without rock, and after 1-2 sec engine sound stop too.