TexasCHLforum.com

Here is a link to explanations of weight rating terms. The site also has links to weight calculators.
http://changingears.com/rv-sec-tow-vehicle-sizing.shtml" onclick="window.open(this.href);return false;

Also it is a good idea to work with actual weights as much as possible. Take your truck, with a full fuel tank and all the people and cargo you will normally carry, and have it weighed on a certified scale. You will probably be surprised at the difference between the advertised weight and actual weight.