All Tricks
How to unlock: enter FIDDLERSELBOW as your profile name.

All Vehicles
How to unlock: , enter your profile name as GENERALLEE.

Champ
How to unlock: Enter REDROOSTER as your profile name.

Max Stats
How to unlock: enter your profile name as GINGHAM.

All Challenges
How to unlock: enter DOUBLEBARREL as your profile name.

All Riders
How to unlock: name your profile BUBBA.

All Tracks
How to unlock: enter ROADKILL as your profile name.

Everything
How to unlock: Enter your name as GOLDRUSH (or GOLDDUST).

Vehicals
Enter GENERALLEE as your profile name.

Dimension, Viper, ATC ATVs
You need to complete the ATV Academy & Trick Training objectives to unlock the Dimension and Viper ATVs. You must win at least 8 racers in Arcade to unlock the ATC ATV.

Full stats from the beginning
To get full stats when you choose a name make it goldennugget or golddust both will do the same thing of giving you full stats