Well, since no one has mentioned our shifter, I'll have to leave that alone... but I will say this:
The fact that you implied that the missing shifts problem is a recent development suggested to me that the clutch cable could be stretching or the clutch quadrant is worn out. (if it's still stock) Personally, I adjust my clutch so that there is a little bit of tension in the cable without my foot on it. That way the point where the clutch disengages is fairly high.
As previously mentioned by someone else, I pre-load the shifter, kick the clutch pedal (no where near the carpet) and rip perfect powershifts! But as stated, I don't use the shifters that other people in this thread are recommending. Not that they are bad, I just use a different shifter.