Tires: Tire Upsizing, alloy rims, rim size

Question
Barry, I have a 03 Silverado 2500HD with stock alloy rims.  The door panel says 16 x 6.5, but I bought it used with 285/75R16 on them and they run fine.  Now I need to replace and want the same size tires.  Are all brands of 285/75r16 the same dimensions? I see that the approved Rim Size for a 285 is 7.5-9.0.  Three Q's
Could the Stock Alloys be wider than the door indicates?
What are the Risks of forcing a 285 on a 6.5 rim.
What options are there if I want the widest tire available?

Thanks You guys are GREAT

Answer
Stu,

1)  "Could the Stock Alloys be wider than the door indicates?"

No, my book says the same thing and I believe it.

2)  What are the Risks of forcing a 285 on a 6.5 rim."

The tire may wear in the center, and you might have some stability issues - the vehicle may be prone to swaying in the wind or following the grooves in the pavement.  A lot of this is dependent on the tire itself.

3)  "What options are there if I want the widest tire available?"

There aren't any - the LT245/75R16 is the largest tire that fits on this rim