@LRClyde
Using a 4 Gib card should not be an issue, regardless of speed. The speed only relates to write speed. The read speed is the same regardless of the class of card (e.g. a SanDisk Ultra II has a minimum write speed of 15 MB/sec but its read speed is the same in your unit as a lower spec card). However, having an image file of 2 GiB or larger on your 4 Gib or larger card was once very much an issue because many older Garmin units had a file size limitation of 2 GiB. Later fw updates changed that for many units and their limit is now 4 Gib minus 1 byte which is actually a limitation of FAT32. Not sure if the GW and SP units are still stuck with the 2 GiB image size limit. You should try with a 2 Gib card but that may not be your problem in this case.