My 2003 GT Mustang has a intermittent hesitation problem when you try to speed up.The car has around 140,000 miles on it.Not sure what causes this.No check engine lights are on.Not sure how old the fuel pump is or if they fuel filter needs replaced.

 

Pick the low hanging fruit first. If you don't know when the last time the fuel filter was replaced, replace it.

 

I would start replacing the little things one by one, sensors, plugs, coils, wires, fuel filter, fuel pump and go from there. I make it as rule of thumb that when my vehicles start to get up their in mileage its better to do preventive maintenance than wait for something to break and get stuck somewhere.

 

Start with fuel filter. Remove and inspect spark plugs, or if you want just go ahead and replace. Inspect the coil boots while you're in there, if there are any signs of deterioration or whatever they can be replaced individually for about $10 each.