Drill Dozer Cheats

Once you have unlocked the Full Gearbox using the secret room in the tutorial level, you are able to replay any world with all three gears by using its effect. To activate it, hold R and press Select while on the world select screen. The Screw Bit will turn yellow to indicate that you have activated the Full Gearbox.
R+Select --> Toggle Full Gearbox on World Map screen

Once you have the Proof of Mastery item, you can select Hard mode on the file select screen by holding down L+R before you hit the Start button.
L+R+Start --> Hard mode