sounds like a combination of sloppy shifter bushings, and a loose clutch cable, or just worn pressure plate. My car is like this at 260,000 miles, and the clutch will slip in high gear at highway speeds if i force it. Shifting it is like rowing a boat and throwing ahot dog down a hall way.
In my case the sloppy bushing is on the shifter shaft, comes as a unit, and is secured by a roll pin, and is a 60 dollar preassembled part at the dealer, for which you cannot get individual bits for, and cannot service unless you drive out the roll pin and remove it from the trans.
Try double clutching techniques. First check the clutch cable adjustment as it has to be adjusted to compensate for clutch disc wear.
Edited by MilesFox, 13 February 2014 - 08:56 PM.