theres a spring underneath, runs from frame to transaxle input shaft, adjusting that can help.
theres also a damper ( Part # 426012M91 basically a shock absorber that costs approx 155$) that when old acts all funky. often times it sticks causing hard to move as well as no return when letting off pedals.
theres also a bearing (part # 6254105M1 iirc was 15$) on side of frame right behind cruise control mechanism that holds on end of the pedal input shaft into transaxle. that can really cause a no return issue and is a PITA to replace.
I've replaced all 3 but there is still stiffness, but pedals don't stick down anymore.
at that point if I wanted easier I'd prob have to open transaxle and look at input end inside. not worth the money.
one thing I did was the 2400 fwd pedal has 2 mount holes, I raised pedal up (mounted to shaft) by bolting pedal on using the lower bolt hole. raised pedal approx 1.5" and gave my foot more leverage.