13.6 is a slow run for any srt6 imo. I ran 13.7 once because I slid down the first 10 or 15 feet of the track then bogged a lil. I ran a 12.8 too but the track I was (MIR) is almost at sea level. Granted my launch tecnique was'nt the greatest (mash the gas and go), but I was happy just being in the 12's with the same mods as you.