I have a 98 neon SOHC with an automatic trans. I have a very stiff gas pedal only when its in drive. It seems to go to about half way fine but after that you have to press it very hard to open all the way. When you do this the transmission develops an issue. It wont shift out of second gear until your going about 90 km/h. Also as soon as it drops down to about 80 it shifts back into second and its a bit if a hard down shift. If I stop and put the car in park and then back into drive it shifts fine but the pedal is very stiff again. What they heck could be going on?

 

Your kick down lever is getting stuck for some reason. The cable runs from the throttle body to the transmission. Do not force this arm! You can run into big problems, been there done that. Make sure nothing is blocking the arms travel path and the cable moves freely. Try some PB blaster on it and work it back and forth lightly. If your not to familiar with these take it to a shop and tell them what i said. Don't force it!

Wanted to add the kick down arm is on top of the shifter level in the transmission. It works in conjunction with it, thats why it changes based on where the shifter selector is. But the two arms should move separately, and they are not.