If your car seems to have an exceptionally hard gas pedal, you probably aren't getting the required amount of air to the intake, and that leads to sluggish performance. You can probably spend quite a bit of time trying to figure out why. Well, here's why. Seems that over time, with usage and heat from the motor, your throttle cable (from the pedal to the throttle body) can stretch. If you've ever seen one it's frightfully thin anyway, so it makes sense.
To confirm that your throttle cable is stretched, make sure the car is in Park and that it's off. Next, remove the insulation panel above the gas pedal. Then, get yourself a flashlight; you'll need it to see the pedal up high under the dash. Unfortunately, you have to squeeze in under the dash just like you're changing a fuse. Shine the light up on the accelerator pedal shaft. There is a black grommet on the top of the shaft, with the throttle cable inside that grommet. At rest, the metal cable end should be pulled tight against the grommet. If you see any additional cable sticking out from the grommet, or if there's a lot of play if you wiggle the gas pedal, there's your problem (see arrow in photo).
You will obviously need a new throttle cable. If the pedal's been feeling this way for a long time, you may also need to get a new kickdown (a.k.a. throttle valve or TV) cable to the transmission, if your Cougar is so equipped. Or, if your Cat has linkage, you might need to either adjust it, get new bushings for it, or replace it altogether. Why? If your throttle cable is stretched, that also means your transmission linkage may be stretched too. If you don't replace the cable or linkage, then you will cause long term damage to your transmission, requiring the dreaded rebuild. A new throttle cable is usually around $30-40, and the kickdown cable should also be around the same. The linkage is more money because there are more parts involved in the system. You will need to check your local parts store for your particular transmission and model year, as linkage differs greatly.
If you cannot find the cable(s) or linkage at your parts store, then you may have to dig deep at the dealership or on eBay (be aware that many other Ford models used the same cables). And if THEY don't have one, your only choice will be to fabricate your own using a universal kit. Lokar makes universal and some transmission-specific kits that may be useful.