Few quick questions...

On my 96 GMC sierra x-cab can I run a rs-62? Or do I need to go with the rs-72? I'm running Firestone 2600 right now but I am having some clearence problems, guess I didn't cut enough after all and I'm not wanting to cut anymore than I already have. The bag fit fine BEFORE I put air in it, almost like it swole up on me or something. Already blew one but luckily I had extras and I replaced it, aired it up , and noticed the rear touching a little. I was reading on the Slams and they don;t seem to change their diameter at all. The rs-62 is 6" I think and the 72 is 7", whats a Firestone? I know this is alot to read but I am trying to explain it all. Also where can I get cups for a Slam bag? I need as many answers, or opinions as soon as I can get them, need this truck back on the road sooooooon!!! Lol my daily driver died on me. Thanks in advance.