What about adding it into Int and creating a new skill for the use of their new tool such as "First Aid" or "Medi Tech" skill which allows them to use stim packs without OD'ing themselves etc. Medi Tech could also effect how well you use med kits. (but not by much) EG you'd need say 40 points to cap med kits and use stim packs (This would mean tank's would still be using psi).
Or if you put it in dex make it so tanks cant use any rare pistol and rifle weapons and cant use non-rare that well, then put in an agility cap in? We could see "Recycle tanks" and "Repair Tanks"