Why did my times drop?

First of all, yes I know I was running my Chevy this weekend but I still need help. Mustang has broken clutch...

Last time at track I ran 13.00 at over 106. Fast!!!
This time I ran consistent 14.70s at around 94. Slow!!!

Since the last time at track, car recieved a whole new painless wiring harness including new battery cables. I put in a new MSD HEI coil, cap, and rotor. I installed a new MSD digital 6 plus ignition. I advanced the timing about 8 degrees. I put .1 more gap in every plug. I installed new russel carburetor fittings and an inline filter. Plent of pressure at carb too now ( around 8 psi.)

The only thing I didnt use this time was really good gas. I just used 93 octane.

But to drop 2.00 seconds and 12 mph? What sort of this should I look for?

It is sort of tricky to answer but ill do my best.

I was running 8 degrees advance. The first time out on the strip with that timing I ran 93 octane gas. I saw good 13 second times and 105 mph plus speeds. Next time out same thing but I ran the car with about 50% pump gas and 50% 100 octane in it. It ran better but not hugely. I got several solid 13.00 times. The car should be running easy mid to high twelves though.

This time, I put the timing at 15 degrees advance. Remember also pu all new ignition in. Didnt notice any pinging at ful throttle so went ahead with 93 octane. Times went all to *****. It also felt a little like it was having trouble spinning up to the higher RPMs, 5K plus. I hardly made it into 3rd gear.

Could advancing the timing and not running the good gas do THAT MUCH? 12 mph drop in speeds?