Yes, Garmin tend to use the umbrella term 'software' for their unit firmware, which it is in fact of course, just a relatively small and specialised piece of sw more closely associated with the specific hardware than general software may be. Goddam confusing for many users and beats me why they [and others] do that.

The 4.90 fw is the latest version for 6x0, the other minor fw versions don't count for this puzzle, but on a side note some of my 3x0/6x0 units are running 'GPS SW VERSION 3.00' and others have V2.90 and those units aren't offered V3.00 for some reason. However it's immaterial anyway.

Perhaps we should look at the particular card you're using. Have you tried any others apart from the Kingston 8GB Class 10? I've really don't have a clue why this is happening for you. Even the 2014.40 shouldn't work either at 2.10GiB but we know it does on different brand and size cards regardless.

As to the Ford PCM, older ones had a known issue with corrosion to the connecting pins because of a dumb location letting moisture in. PM me if you want the solution. I won't tell you where the MMs grow though seeing you're from NH not MA. Nearly as many freaking' Deerfields in US as there are Springfields i think .....