I don't know where you people are getting your info. But the new edge GT's definitely do not have had governors on them, rev limiters yes, but there is no speed limiters on them The V6's might be governed to around 107-112 for tire speed rating considerations. But the V8's are not. When my 03 GT was stock It exceeded 130 MPH and had a little more in it before I ran out of road.
As for why you're topping out at 120 MPH, if you have the stock 3.27, you should be shifting into 5th at about 125 MPH. If you're shifting into 5th at lower speeds you'll drop the engine into a lower RPM range where it doesn't produce as much power. The P.I. 4.6L in the Mustang makes it's peak torque around 4000 RPM and the HP peaks at just after 5000 RPM. When you take into consideration that the 5th gear is either .62 or .68, there's a lot RPM drop off when you shift into 5th. If you're only turning 3200 RPM in 5th gear (which equates to around 126 MPH on a stock 03 GT), it's going to take a while to get the last 10-15 MPH out of the car since it's out of the RPM range where the engine makes most of it's power.
From the factory they govern them at 120 because.Why ? Police cars blow a transmission seal at 135 to 140 and they don't want us being able to out run them. Think about that lol feel free to leave feedback. You will either have to pay someone to reprogram the computer or buy a tuner yourself. Another thing is sometimes a a performance chip may include this option. Try asking your local performance store or the net you may find what you are looking for. That is your options hope this helps feel free to leave feedback.
Most cars are governed depending on the year make and models and some are not. If it had something to do with the gearing of the car and the rmp it would still wind over the 120 mark in fifth gear unless it is red lined at 120 . If you still have peddle at 120 and you push it farther and wont change anything then it is governed.
It's the governor, they made it mandatory for all cars to have governor so speedsters werent aloud to race excessively. Some are set at different speeds(I.E. mine kicks in at 150) it can be taken of if you reprogram your ECU.