3000 x 3000 is fine it's the megabytes. To get around that, when you "save as jpeg" in PS you will see a slider that goes from 1 to 12...that's the image quality slider. Move that down to 11 then 10, sometimes 9 is needed to get those megabytes down...got to be like 4.7 megabytes. The actual quality lost can't really be seen until you get down to like 6. Nearly every map I do is uploaded at 10 or 11 and a few have been 9s.