I think it is the servo too but make no sense ,It oly act wierd when the servo moves ,even when i lift the front and no weight on front tires so the servo work easy seems no problem but as soon it has some friction akt stupid .I suspect the radio receiver bad or the servo .
like I said, a bad servo can do wierd things. most of the time when a servo goes bad, it simply doesnt turn...as the gears get stripped. but if the internal board goes bad, it can effect the reciever's function and thus effect the speed control as well.
If you pull the servo plug out of the reciever and test to see if the throttle works right (turn the wheel on the radio as well to make sure it doesnt effect throttle control like it was in the video)
If the throttle control works fine with the servo plug pulled from the reciever then you can know for sure that the servo is bad.