I have a 04 2500HD 2WD and I was thinking about going with 265s when my stock tires wear out. What wheels should I get? 16 x 8, 17 x8? What is the right back spacing etc.? I saw Weld has some wheels that are 16 x 8 and rated at 4000 lbs. Will I have to do any clearancing if I get the right back spacing? I want to get the best stability and weight handling I can while still having a fairly normal looking truck.

I have no answers to your questions, but have a question to ask: Do you really need new rims? I bought some Michelin 265's, put them on the stock 6.5" rims, and stability seems to be fine with my heavy fifth wheel-- and I'm at/near my GCWR of 22k lbs. Wider rims will no doubt provide greater stability, but do you need it? My stock rims match the 3400lb rating of the 265's, so all seems well... If I were bying new rims anyway, THEN I might consider bigger/wider rims, but I like my aluminum wheels. Just my opinion... --Paul.

All 265 tires I have looked at, the manufacturer recomends a 7 to 9" rim and ratings are given with a 8" rim so I assume weight handling is reduced with a 6.5".

I up-graded to Michelin LTX M/S 265/75/16E. Any larger 16" tire l found was not E rated. 3415 lbs each.
I considered a 265/70/17E, (the lower sidewall should be more stable), but these were only rated to 3200 lbs each.

As far as rims, many run the 265 on the stock 6.5" PYO, but I was also concerned about a decreased load rating with the narrow rim. Also much discussion about the PYO load rating seems to think the PYO is only rated around 3100 lbs, but I don't know where to verify that.
I purchased the Alcoa Classic 16" by 7" wide, one piece forged, rated at 3750 lbs each. Cost $150 each with centers, nuts, and nut caps included. Only disadvantage I know of is that they are not a coated rim, so you may have to polish them anually, especially if you run them in salt in winter.

What backspacing do I need so I will not have any clearance issues?

depends on how heavy and how many miles??

The heavy towing statement leads me to believe you should stay with the 245's for the gearing advantage. It is trivia, but noticable.

i am looking at the 265's for the increased load capacity of the tire.