Is it really necessary to keep repeating the !also /use 13 & 14? In my similar 2-Step (now 3-Step) setup I've just added:
Code:
/use 13
/use 14
into the bottom of step 2, just before turning the error frame back on. I also use, at the beginning of Step 1:
Code:
!if (character in "Melee") /startattack
I personally find that fewer conditionals, and the combining of conditionals for similar classes, reduces the likelihood of making an error during later edits.

While I'm not certain of the value of a Tri-Step system, I started using it because I was unable to reliably get my Blood DK to cast Bone Shield and Horn of Winter or get my Boomkins to shift form quickly enough on non-instance trash. Tri-Step gives me another /castsequence and/or /cast fallthrough set to play with and, once everything is inside ISBoxer, maintaining multiple DPS steps becomes trivial.

For those interested the ISBoxer 38 Beta adds a new keystroke action called "Named WoW Macro" which can be used from a keymap. Individual macros work in the same way as ISB 37 but new "Macro Sets" and a centralised repository of friendly named macros make this stuff FAR easier to manage.