[A/S] transmission heating

["jazzeriqua" <jazzeriqua@xxxxxxxxx>]

Hi!  We have a 2004 Suburban 3/4 ton with 3.73 axle, towing a 25' 
Excella.  While we were towing it up to a ski resort at about 7000ft, 
a warning flashed on the dash about the transmission getting too hot.  
The manual says this warning should only show at over 265 degress and 
the gauge showed only 200 degrees.  Does anyone know if this is a 
known problem?  Should we only tow in 3rd, not in overdrive?  If so, 
then why or when do we use the "tow" button to change how the 
transmission shifts while towing?  Any ideas?