my 2015 Ecoboost mustang 6 speed auto just had the engine rebuilt and I got the car back last month. Since I got it back I noticed the car to be a bit sluggish except for when you manually shift it with the paddles. Today, the transmission started to act weird, it didn't want to go past 3500 RPM in 3rd gear nor did it engage 4th gear. I'm not sure if it went into limp mode or if the tranny or engine are damaged.it happened right before I had to be to work so I couldn't test it any further. Didn't see any engine lights or flashing wrenches on the dash display. what could it be? I don't have tools on me, I'm at work right now, so I can't really check the tranny fluid.