Couple of questions and suggestions.
1. How much wheel hop are you getting? before I put my LCA's on about 2 and a half years ago I had wheel hop bad and traction stank.
2. When I dropped my car I also used a relocation bracket for my LCA's and UPR double adjustable upper control arms with a few other goodies
(That will help out greatly) LCA's to start with as I understand it's all expensive.
3. If the P-zero tires are not cutting it, try some Nitto NT555 I Graduated to those about a year and a half ago and I drive my car like I stole it and still have good tread left. Expensive, but down the road it may help you out.
4. One of the cheaper items to try - Talk to MPT about getting one of their tunes. I switched from Bama and it was night and day difference as my car accelerated faster and got to high rpm's much quicker Only 75$ and might make you smile again about your Mustang. I had a 93 Hybrid tune from Bama, it was working fine, but I wanted more and I heard a lot of people having good experiences with that tune.
5. One of the mods I recently did was the BBK throttle body 73mm. This made a huge difference with the mods I already had and I'm ripping up to high RPM and I actually chirped today in 4th gear, even though a little baby chirp it was impressive
My suggestion is to get the traction take care of, if that's an issue, and then try a different tuner 75$ is worth a shot. BBK throttle body will help with 1800-4000 rpm.