i had a very similar issue. It was due to the air filter rubbing on a ground cable and it eventually broke the ground cable. That ground was for the computer that controlled ABS, AdvanceTrac, etc. So take a peek under your air filter and make sure those two ground cables are still good...
2015 Ford Mustang GT Premium and Performance Package. This car pretty much has every option that Ford offers. It's always garaged, adult driven, never abused. At Whipple Dyno Day it did 656rwhp and 521ft/lbs. It's incredibly fast and still actually turns a decent MPG on the freeway. It's all CA...