Chevy/GMC vehicles actually have a Tow Mode button, and I would love to have some technical detail on exactly what it does. I believe - and I have no substantial backup for this - that the Tow Mode does a couple things. First, it changes the shift point RPM, much like you are doing manually on your Toyota, Rickst29. Second, I think (I hope!) that it causes the torque converter to lock up more of the time, spending less time in the partially-locked states that are normally used. The partially-locked states give a more comfortable ride because they simulate a whole range of partial gears between (for example) 3rd and 4th, or between 4th and 5th. But partially-locked is also a heat generator, and becomes a real problem with the extra load of towing a trailer.
Ford (mine, for instance) and other vehicles have an Overdrive Lockout button, which simply tells the tranny not to use the upper gear or gears. But as near as I can tell, behavior in the lower gears is unchanged. I don't believe that this is the same as the Chevy Tow Mode.
If anyone has access to a comprehensive description of what Chevy's Tow Mode really does, I would love to see it.
Bill
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