[A/S] overdrive use with dodge truck auto transmission

["nickcrowhurst"]

I would appreciate advice on when to use overdrive when towing a 6500 
pound 25 foot Airstream with a 98 Dodge 2500 long bed extended cab 
truck with auto transmission. I have examined the truck manual, this 
list's archive, and that of the Turbo Diesel Register, and I'm still 
not clear on this. I have only towed so far on the level roads of 
Florida, when I have used permanent overdrive very comfortably. 
Without overdrive, the engine seems to be over-revving and noisy. 
Presumably the situation would be different on steep up and down 
grades. I aim to keep the truck for ever, and wish to care for the 
transmission.I would appreciate the wisdom and experience of you good 
folks with the Dodge auto transmission. Thanks, from Nick.