Just completed the same 20km trip home in reverse. Left the 3590 in the glovebox, and used the 3790>3490 only. Cloud a little less, more few-scattered (2 to 3 eighths of sky covered) whereas outward trip was more like half sky covered. Mostly 5 metres, but sometimes 4 or very occasionally and briefly 6m. Acceptable accuracy and consistent. Very light traffic, only took 20 mins and able to watch the screen safely. So what's different in other users' units from Caty's and my unit, why are some ppl experiencing and reporting such high inaccuracies? I have a good chance to get a 3790 in the next few days to make a proper comparison.