speedo way off after gear change

[csracingmustang]

Hello,

Working on a 2004 Mustang GT for my son. We just changed the ring and pinion to a 4.10 ratio. I updated the gear in HP and reflashed it. It was off a little more than 10mph. Went back in and noticed that the tire revs per mile was 812 for a 235/45r17 tire. I looked up the revs per mile and found that 821 was a better number. Entered that number and now it's off by like 25mph. Transmission VSS is 24 teeth per revolution from what I can find on the 4R70W, which matches whats in the calibration file. I'm at a loss for what we're doing wrong here. I can guess and check on revs per mile on the tire to get it right but this just doesn't seem like the right way to do it. Ideas?


Second topic, being an older car we wanted to disable PATS. I selected PATS disable in HPT but when we flashed the file the theft light flashes constantly. Can this not be disabled on this car?