410 LA small block will not rev past 6000

I have a 1972 Demon 4 speed, 3.91 gears,
* Edit 5252 rpm don't happen at 88 mph cause hp and tq are scaled different on this graph so this is all wrong.


90 mph obviously pretty much equals 5252 rpms, 90 x 336 x 3.91 / 5252 = 22.5" now I don't know why it comes out to a 22.5" inch tire, low air pressure, I did it wrong :) ?

But at a 113 with a 22.5" tire I'm getting 6598 rpms = 113 x 336 x 3.91 / 22.5"