By chance do you know for sure they are the same "COMPOUND" tire? I had the same thing happen to me last year. I bought a new set of 14x32x15 M/T and i fell off a ton. I put the old one back on (they were still good, kept for backups), and it picked back up 4-6 hunds in the 60'. Come to find out the great deal i got on the new slicks was for a harder compound tire. Just a thought.