There is a position between the high gear and the "normal" where there is no drive. So you would be able to pedal the high gear and hear the pawls ticking, and see the wheel going round faster than the cog. So pull the chain past the first slipping, and you should have middle or normal gear, where the cog is turning the same speed as the wheel.
A further pull should engage low gear, which seems to be slipping, and it seems as if your pawls in the left hand end plate have stuck, or the pawl springs rusted away. You can take the LH cone off and remove the LH end plate to see this, it is left hand thread, and has 2 large flats on it. If you find the pawls are not working it would be better to take the hub apart from the other end, but a little oil while the end plate is off might work.