what would cause this?

Friday went to pick up kid from school and was running dm. On 93 octane I got 1.6* kr max. Went to the track sat. and made 2 passes got 15.5* max kr on both passes. Just made a run while at work and got 0* .All of the runs were on the same tank of gas with no changes to anything. What would cause this much differance.
 
I had turned the truck upside down looking for loose stuff and couldnt find anything. Also there isnt anything rubbing. this is driving me up the wall :( It would be so nice to go to the track and get some good numbers.
 
Well I may have found my kr. Was working on the truck and noticed a spot on the pass fender well that the down pipe is hitting under a load. It has to move about an inch to get there. So Im guessing that the mounts are shot. Got the JS & energy sup. Now to get of my ass and put them in. Would stainless steel make a good heat sheld? I dont want to put them in just to have them melt.
 
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