The second race you listed was the Infineon Memorial day race, right? I don't know if I would use that for a case of car inconsistancy. Measuring wind speed I was seeing a headwind of 4-7MPH at the last time trial, 10 to 15MPH in the first round and the same with gusts to 20 in the second round. My car started the day with a 10.36 and was running 10.44 in the first round. Days like that I just sandbag, play the top end and hope for the best.

Another thing about Infineon, they always have a long break (sometimes 2 hours) between the classes last time trial and eliminations. Keep a close eye on oil and trans temps. I like to drive the car around during the break like it was morning pre-race warm ups. That seemed to help out alot with first round consistancy.
-Tom.