Hi David,
If the reading is low rather than high the ECU would call for less fuel than required, the difference between the reading you have and optimum is pretty slight but could still under fuel the engine I guess.
Did you check the reading with the throttle wide open ?
Engine doesn't need to be running for this, provided the ignition is switched on the TPS will be live, just hold the throttle fully open and see what voltage you get -
Maybe clean the air flow sensor next, nice easy job but be careful as the filament is quite delicate.
Use electrical contact cleaner and a cotton bud as described on the mustang forums.
Good luck,