Am I missing something (nuvi660)

Hi,
Well, I've during last two years a nuvi 660 that I think it's very good on
routing by the highways.

Some times like this year I wanted to travel not on the highways but in the
main roads (we call it national roads in Europe) but not on third or fourth
category roads or even in "farm roads".

I thought this was a simple thing to ask my nuvi to do, but I was wrong.

This happened to me this year in Pyrenees and south of France. Am I
missing something? I have the latest firmware and Europe NT 2008. My
settings are:

"Car", "Faster Time", unable "highways" (put a check in the highways box, in
the avoidance menu).

I've tried to change "faster time" to "Shorter Distance" even I change "car"
to "truck" and "bus" hopping that the gps could "see" that truck or bus are
much bigger than a car.

Yes, if I had bus I couldn't pass through some roads I have passed with my
car.

Am I missing something?

Thanks