What's your RPM?

As Mrmopartech said, re-set the tach, measure your rear tires for installed height, and post the numbers. You might also check on the rear end itself to see if there's a gear ratio tag still attached to one of the cover bolts. That's a very nicely done engine bay you have there. :) Also, I ran a 7.25" rear end for about 15 years in my Vart behind a well warmed over 360 and it's still in great shape, although she gets a 8.75" this time. The biggest things to keeping the 7.25" alive (1) absolutely NO brake stands. If your foot is on the brake, don't touch the gas pedal. That's how my first one expired behind a hot 318. :) (2) Don't punch it going around corners cause they'll spit those little side gear teeth right out of there. Good luck.