[Jeepwm69]

Check the rear end. Same crappy design as the 300 with the open axle.

Other than that the 420's are pretty good machines. 4th gear going out seems to be a recurring problem in early models that have been abused. Downshift and give it throttle between 5th to 4th, then 4th to third, see if you feel any "skips"

 

[Jeepwm69]

Well if it's brand new it will be obvious that it is new, so that's good.

Check and make sure the gears all catch well both upshifting and downshifting, and if it runs well it ought to be good to go.