missing shifts. clutch adjustment?

Try screwing the firewall adjuster away from the firewall. That makes if engage further from the floor and easier to shift. Also now that I have switched back to a ford cable from the steeda one if seems to be smoother.

I and most others have found aftermarket cables to be junk. I had a Steeda cable that rusted BADLY within 2 years. Use an OEM cable.
I really doubt your issue is related to this however. Are you having any issues shifting during normal driving? It's likely driver error. No offense, but quite honestly that is typically the issue. You are simply trying to shift too quickly and not properly synchronizing your left foot and your right hand.

get rid of the adjustable cable....mine did this same thing.. got to the point where i couldnt go higher than 3 grand cause i wouldnt be able to get the shifter out of gear after that point... whether i was at WOT or not.. plus it got to the point to where it took every ounce of strength i had to get it into reverse and it was difficult to even get it into 1st.. after a while, under normal driving, i was fighting to even shift gears...

get rid of the adjustable cable and i guarantee you will be able to go back to normal, smooth shifting... this problem occurs A LOT with the steeda adjustable cables, but i know of a few others with other brand adj. cable that did the same thing...they switched back to the OEM and problem was solved...if you dont trust OEM, but MM non adjustable cable