Tires: New Tires, stock tires, tire calculator

Question
I have a 2003 Dodge 2500 Quad Cab Diesel.  My stock tires are 265/70/17.  I was thinking of putting on LT285/70/17.  
Do I have worry abour the speedometer or any other technical issue.  My truck does have a leveling kit on it already.  Please advise.

p.s.  I do pull a 28ft travel trailer with my truck.  My truck does not get used much, only on weekends.

Answer
Brian,

You should spend a bit of time with a tire calculator:

www.1010tires.com

Look for the words "Tire Calculator"

You want to be careful about the diameter ( + / - 3% is the usual recommendation), the rim width - yours are 8", and the amount of space in the fenderwell - sorry, but that's something I won't know about without measuring your truck or looking it up in a book, and the folks that have done the measurements seem to feel that gives them a competitive advantage and they don't publish the info.