You got a 14.7 at 91MPH? Wow I can't even break 15 usually at 95

Damn I need gears hehe. Anyway.. have you considered the possibility that you are losing fuel or pressure at high RPM? The stall speed wouldn't matter at high speed, it's for launching. If it's possible hook a FP guage to the rail and route it so you can see it when you are driving fast under load (accelerating) and see if it drops. This would be my first step. The fuel pump might be going south especially if it's original.
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87 GT
Full exhaust, K&N, KB Subs, BBK STB, homeade dumps...
87 Taurus
New York
Winters Bite!