[Phantom]

Matt,
According to the manuals your 2+2 has the same 4-spd and rear differential as the coupe.
That means that originally you had a 3.545 differential which would give you about 80 mph at 4,000. Even installing the earlier 3.364 ratio would only get you to about 85 mph at 4,000.
something isn't right here.
Phantom

 

[Phantom]

> If you are running larger (taller) tires
> than what came stock, it could account for
> higher speeds at lower rpm. I did this once
> on my Honda because I wanted to cut the
> rpm/speed ratio to improve milage and reduce
> engine wear, but for the next set of tires I
> went back to stock because the power
> suffered with the little engine and the
> milage did not improve. The rpm/speed ratio
> is linearly related to the tire height, so
> you can calculate where you are relative to
> stock tires. Cops love this one when they
> pull you over.

Kane,
For him to know that he's doing 90 I would asume that his speedometer would be indicating that. The taller tire speed increase would not be reflected on the speedometer.
Phantom