I am having a weird issue on my 07 Mustang GT, 4.6L, 5 Speed. In first gear the car stutters and tries to stall with AC on. I have changed the fuel filter twice, the sending unit works when it wants. The malfunction of the sending unit does not correspond with the fuel issue. I started to notice some hesitation in 1st without the AC on. I am going to change the filter one more time, but I am suspecting the fuel pump. Regulator is good according to OBD reader.