WOT Sticking

I've got an '86 GT and when I hammer on the accelerator in 1st gear the throttle sticks wide open. In order to clear it, I have to kick the pedal (sometimes repeatedly). I've checked to see if it was binding on the floor mat and couldn't find anything. A quick check of the throttle cable doesn't indicate any kinks. The problem doesn't seem to occur in any other gear than first - could this be worn motor mounts? Any ideas are greatly appreciated!

When I move the throttle linkage (under the TB) it moves freely. I did notice, however that the cable seems to lag - the linkage returns to it's original position and the cable then goes 'shunk' (you can hear the gas pedal hit the firewall as well). I'm thinking bad/damaged cable as I don't recall a previous 5liter doing the same thing??? (I did do a quick check of the cable - perhaps I missed something?). Also, when I 'rugged' the accelerator in the car (not running) I heard the same delayed 'shunk' after lifting my foot...

The good news is my alternate transportation is a 2003 F-150 XTR 4x4

Well, I went out last night and played around with the accelerator pedal and cable at the point where it entered the firewall. Some WD-40 and a little bit of poking around seems to have solved the problem. Weirdly enough, after spraying cable and then working it a few times the pedal response seemed normal. A 45 min test drive showed no indications of the problem.

I just purchased the car this past weekend from the original owner's estate (deceased). The guy was meticulous about taking care of it (always serviced at a Ford dealer - full receipts, bill of sale, etc.) It's obvious that he didn't drive it very hard either, as he only had the 1st clutch replaced in 2002. Maybe the car hadn't seen WOT that often and the cable just needed to be broken in (wishful thinking?)??? I'll keep my eyes on it during the summer - but just wanted to say thanks to everybody who replied!