My XLS shows 19.6MB free RAM here at home under static conditions. I will check it underway to see if it changes.
I don't have any third party software installed.
How about the size of your SD cards. Trying to write to a card of more than 4GB can lead to impredictable results on ONE models. I'm fairly sure it can read it right but writing is a different story. Writing occurs when having to recalculate a route because you don't follow the planned route caused by road blocks, going for gas or simply wishing to veer off course. On my last 5 hour trip, it must have recalculated at least 15 times but the computer voice never stuttered and only had radar POI notification active with my 4GB TopRam SDHC card.