I think Kenny is right. If the electronic compass is turned on and isn't calibrated properly, it will cause the cache direction pointer on the map screen to swing wildly when walking to a cache. As you are moving, the unit used the changes in GPS position to determine your direction of travel. As you slow a bit, the compass takes over and, if it needs calibration, can cause it to suddenly point the other way. I had trouble with this on my 64s when I first got it and had to recalibrate several times a day and it drove me nuts. Finally, they did a firmware upgrade that seemed to fix it, for the most part. I still try to recalibrate whenever I change batteries.
Additionally, when recalibrating, make sure you are out in the open and away from any metal objects. Mine always fails on the pitch axis if I try to calibrate it in the house or while sitting in my truck.
My Nuvi 550 does all that, but it's an older unit and has begun exhibiting the same symptoms you mention with the intermittent connector. I don't think Garmin makes a Nuvi anymore that is considered "geocaching friendly", but you can do a lot with GSAK and the POI loader macros.
The Garmin Montana will do what you want, and holds up to 15,000 caches. You can even set it to be in Nuvi navigation mode when in the car mount and then switch to hiking/geocaching mode when out of the car mount. Unfortunately, they're even pricier than $450...
I've noticed how Google Earth now displays in this pseudo-3D view, but garbles everything. I was looking at the unit we built at Exxon right before I retired. I swear those pipes were all straight when we built it!