I recently went to the track and just wondering why mph are different

01 ITR
skunk 2 stage II cams
skunk 2 springs&retainers
skunk 2 cam gears
vafc
jdm 4-1 header
aem cai

The elevation here is 3900 ft
I ran it a few times and best runs were
14.6 @ 93
14.6 @93 then I ran it for the last time and ran a
14.7@96 mph. just wondering why my time was slower and mph were faster. Am I doing something wrong? My 60' were 2.1 every time