Joe, my overall answer to whether you should get a board specifically for TS is "maybe."
It depends on several factors, mainly how long your wheelbase is, how tight the courses you usually ride are, and how big your feet are.
ConeKiller HS
Overall: 8.75" x 32.5"
Wheelbases: 19.5" to 21"
The wheelbase (inner hole to inner hole) on your ConeKiller can go from 19.5" to 21". For some people, the 19.5" is short enough for TS. But if you're riding relatively flat courses, your cone spacing is probably pretty tight (< 6 feet between centers), and that board may end up feeling a little big and sluggish.
One other thing that may be affecting your performance (in addition to perhaps just continuing to practice, as Donald recommends) is your big ol' honkin' feet.

It could be that the Skaterbuilt is just too narrow where your feet actually contact it to give you proper leverage. If you angle your feet forward quite a bit, it will probably work just fine. But if you have a more surfy stance (feet across the board), your feet will not be well supported, as the CK gets pretty narrow there. I used to think a narrower board and/or very narrow trucks meant a better TS board, but in the end I found that a wider board and trucks (about the size you have) gave more leverage, which resulted in an easier (and thus quicker) turn.
Kramer (forgive my bad Photoshop outline/cut)
Overall dimensions: 31" x 8 3/8" (7" tapered tail width)
Wheelbases: 18.625" and 19.625"
The Kramer model puts a bit more "meat" where your feet are likely to be, and it has a shorter wheelbase option. So my guess is it would feel a little more secure underfoot and give you a better/quicker feel.
That said, you might even consider an even wider board, something like the Fullbag "Junk in the Trunk" TS model:
This would put even a bit more width under your feet than the Kramer. But alas, only you can tell how much is enough or too much. Note: Fullbag boards have a mellower tail kick than either the CK or the Axe boards. It's a bit more of a pocket than a kicktail. But they are top quality, just as the Skaterbuilt and Axe boards are.
Bottom line: Try to work with what you've got, and if you have any friends who ride wider boards with short-ish wheelbases, try every one you can and see what fits your style best.
Hope that helps.