You should hook a diagnostic analyzer up and see what the computer sees for rpm. I've noticed that my 00 SVT's tach is "lazy" above 6000 rpm.
The cutoff is 7096 rpm (Ignition/soft limit at 7000rpm) per computer's readings and the tach is maybe at 6900...

2000 SVT #674 - Check it out!

Whoever coined the phrase; "If it ain't broke; don't fix it" ~ Just doesn't get it...