I believe I found the problem... and sorting the file to ensure that all of the individual positions were in correct time sequence seems to be the solution. There were a few records OUT of time sequence, and one or two which had the same exact time on them. When I went through the file and found those that were out of place, and those that were identical in time, even if different in position [I looked at every 30 and where they were not 30 seconds apart I looked more closely and moved or removed the incorrect entries, or inserted missing entries to ensure one entry per second] and fixed the whole file, and THEN added the speed, it loads just fine. So the key likely is the need to be certain that there is no time that should be earlier in the file but is later than other later times. That is a guess, but it makes the ability to sort the individual positions based on date and time even more important, when merging files, etc., if that is what was causing the 'infinity' symbol error. Anyway I am adding a route to the Browse tab called Panama Canal with the full track through the canal, with all of the errors that are in that file due to loss and connection to different satellites, and so forth, over the almost 12.5 hours covered by the track.