@isg
I seem to remember that you said the reported accuracy does not return to the fabled '3 metres' when you reconvert to 3790. But is it really bad when navigating too, i.e. do you have a similar or near-similar crappy accuracy as with it converted to 3490? If so have you tried reformatting internal memory using RMPrepUSB as you said you might try a few days ago?

@dasilvarsa
Your comment about 3490 not 'losing' sat sig in tunnels: I forgot when i replied before to say that it's 'tunnel aware' and it assumes you are travelling at the same speed in the tunnel as when you went in. I find it a bit disconcerting, 'cos you might go in doing 80 klicks in a long tunnel but catch up to a traffic jam going only 20 or 30. Does it then just 'park' after the tunnel exit when it can't re-catch the sats, although it's calculated that it should be outside? Sorry, bit OT here. I think there's a thread, or at least some posts about it somewhere.
I recall Giomen posting about it, maybe do a search for it if you want more info.