There are two solid advantages for tow mode: one, it holds each gear longer on acceleration and if you are in the mountains or "heavy" as most RVs are this can be quite convenient at times to minimize the number of times the transmission has to shift and; two it puts the transmission in a mode to downshift each time you tap the brake. It does not, in itself, cause a downshift or overdrive lockout, it just makes it super easy to select a lower gear for engine braking when in mountainous country. Just try it a few times and see if you like the results. I'm quite sure lots of folks never use the feature and may even not know it's there- and they get along fine without it!
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