frbear I got excited about a handheld NAV a few weeks ago and did lots of research. Almost popped for a Navman (510 I think) before I cooled-down and thought better of it.
I like the idea of a portable GPS still, to be able to use beyond the Ridge, but for vehicular use I really think you gotta have a big screen, else you're gonna squint and lean and poke at your GPS until you run smack-into the tail end of some unlucky person at an intersection or something.
Maybe one of those expensive-but-very-cool slide-out, tilt-up 7" or greater LCD units is the way to go. You'll do whatever you want to do, but I suggest:
1. Take it slow; there are lots of options & wildly varying prices on these things
2. Absolutely go to a Fry's or somewhere that some GPSes are on display, and play with them for a half-hour or more. You will learn very quickly that there are huge diffs in useability between these things.
I assume you didn't buy the Nav because like us you don't have money to throw away (we had to draw the line somewhere, having already spent more on the truck than we'd planned). Be careful w/your GPS idea or you could end-up with a useless "toy".