I have to ask, why would the brake calipers make the gas pedal hard to push?
If the accelerator pedal is stiff you need to inspect all of the throttle linkage and the pedal itself. Disconnect the throttle cable at the throttle bobbin under the hood and see if the bobbin responds as it should, it opens and closes smoothly and has decent spring tension. Now make sure that the throttle cable is free to move in the sheath and lastly make sure that the gas pedal pivots smoothly on it's axis. You will probably find your problem in one of these areas.

Mark