It has been a long time, but,when I had my first 70 Duster I discovered there was a raised "bump" in the floorpan just in the area of the "floating" gas pedal travel and when you "punched" the pedal hard enough it would catch the lower edge of the pedal on that "hump" and would jam in "w.o.t." I do not know if the floor pan profile on your 72 is the same as the 70 but it might be worth checking out.
I cured this by cutting about 1/2 inch off the bottom of the pedal.Hope this info helps, good luck.