Stiff Gas pedal
 

I have an 84 BII and everytime I turn mt truck on my gas pedal goes from nice and progressive while off to friggin stiff when on. It been slowly getting worse over the past month. There is no binding since I have checked all the linkage to the carb several times. Also the pedal moves beautifully when the truck is off, so i know there are no snags. If anyone could enlighten me please do so because this heavy gas pedal is naggin at me.