olejoedad asked the correct question. Too little extension of the slave rod CANNOT be corrected with a longer rod. You almost certainly need to get Rodney's slave!
Searching on clutch does not release will turn up dozens and dozens of threads on the subject....the only common solutions are a bent clutch pedal, the banjo on the pedal rod installed upside down, inadequate bleeding (usually the wrong method), or a bad slave cylinder.
Rodney's slave cylinder ( http://rodneydickman.com/pr...o.php?products_id=66
)was the only thing that fixed the clutch in my '88 GT!
If I were you I would measure how much the slave rod extends (I no certain of the minimum necessary, but I THINK it is 3/4"). If it is less than that, then I would check for a bent pedal, an upside down banjo and if neither are bad, buy a new slave (you WILL need one eventually!