bvalentino

I just recently bought a 1997 Holiday Rambler diesel pusher and am having problems accelerating. The pedal is very hard to push / depress. Any thoughts??? It is a Cummins 325 Also when i use cruise control I have plenty of acceleration. I went back to the engine compartment and checked the throttle and it had plenty of free movement and was fine. I am thinking the problem is in the accelerator pedal itself. Any thoughts would be appreciated. Burt