If you want all NA use a min 4GB SD in the 255W.

I wouldn't buy a 55LM [no traffic], you maybe can get an LMT for not much more but $80 is cheap for a new 55LM.

The ref to gupdate.cgd in the xml is only showing it's correct path, i.e. it goes in the Garmin folder, it doesn't mean there is one there. If you do have a GCD file onboard for V6.70 be sure to remove it before you flash V7.80 in preboot. Name the RGN file only 109101000780.rgn.

Reset by holding the lower RH corner and powering on. Keep holding screen until the prompt to clear all user data appears. Reset both before and after updating software is always safest. Do the 41 backup asap.

P.S. How ya off fer undies and sox?