I know I'm a little late with this deal but it still bugs me what happened.I bought a set of So called Mach 5's from a guy on this site that was good to deal with.I already had mach 3's in my truck so I put the new Mach 5's in expecting to get a nice jump in power and it just wasn't there.I had a feeling that they weren 't 5's and probaly more like 4's only 20 hp more than what I had in the truck.I talked with the seller with pm's and he was willing to work with me.We decided to send them to F1 to varify.Little did I know it wasn't that easy to contact F1 and with my time I didn't get them to F1 for about 10 months.Finally went thru Source and got them checked.They were as suspected a nice set of 4's.So I contacted seller again to see if he would at least help me to upgrade the 4's to 5's what I wanted in the first place.He wanted no part of it and end of story.I don't know he seems pretty knowledgable ya think he would of known they were 4's.What would you guys do in this case..............Thanx..........