Ok so I have a 98 GT with a 4.6 and recently my clutch and brakes got very stiff. I am not sure where to start with the issue. I have checked my brake fluid and I is still full and I didn't see any signs of moisture in it. Any help would be great. Thanks
Except for the pedal assemblies, the two are not related.
For the clutch I'd suspect the cable is bad. Replace with an OE one.
For the brake: How is your power steering? The power assist for the brakes comes from the power steering pump. If you've got a problem there it can affect the brakes. If the steering is fine you may have an issue with the "hydroboost" unit.
I think trinity_gt said it all, but I remember my 91 GT had a bracket for the pedal assembly that broke. May want to just give a look under the dash and make sure all is in order there, could be why both pedals are feeling off since the clutch doesn't use fluid. Just a thought.