I think the answer to MpG changes is relative to whether or not you recalibrate the speedometer correctly. When I upgraded from stock tire to 265/70r18…..my speedo was off like almost 4 mph at 65. At 65mph on the speedo ….gps would say 70.
In My first 5 months of ownership I had many problems with the synch system and the Sirius XM freezing up and not working at all. It must’ve been fixed with a recent update as I do not recall a problem the past month or so. Thankfully.