Hugh, have a helper depress the throttle pedal from in the car while you watch at the engine. After they floor it see if you can still open the throttle any further from the linkage. As the bushings wear out the pedal won't get full rotation at the throttle body and you'll lose throttle actuation (even the bushings in the tunnel can mess with this).
The previous owner of my SC thought it was down on power but the PPI showed that it was just this plus a bent throttle linkage. He was only getting about 70% throttle.
Lots of other good advice here but I'd check this first. I know you said you checked the linkages for being tight but I'm not sure if you checked the full action from pedal to throttle. Ignore if you did.
