also if any one knows what the width of the stock 18 inch rims is

 

Bolt pattern is 6-139.7mm/ 6-5.5''

 

alright thanks

 

Is there any way to easily find out this information online? Tried doing a good search and am having no luck for a 13' GMC Sierra 3500HD (SRW).

 

Check your door sticker. It will show you the width of your stock wheels on there.