For the trucks in the picture, the speed is limited by the manufacturer.
I really hate these trucks. Not for all the genuine reasons that everyone else does. I have a 1995 Geo Tracker. It might have 60 horsepower on a good day. It’s perfect for everything I need it for. Low horsepower vehicles are awesome. Buying a 700hp truck that’s limited at the ECU to 100mph, but you only drive it on 45mph roads, is such a waste. It’s like buying a million dollar house and sleeping in the garage.