Some differences that I remember about the GP and the TMX are that the GP has street tires, street front fender(close to the wheel),the handlebar is not as wide as the TMX's and it there isn't a crossbar,one rear wheel sprocket,no rear luggage rack,no front fender brace.Top speed claimed for the GP is 72 mph.The TMX has street legal knobby tires,a higher front fender,a wider handlebar with a crossbar,two rear wheel sprockets,luggage rack, a front fender brace and the tool kit included a short section of chain-about seven links and a masterlink for use if you wanted to go from the smaller rear wheel sprocket to the larger one.The top speed for the TMX is around 60-65 mph.I am pretty sure there are more differences.