Monster Truck Madness 64 

Low rider trucks 
Enter "YRDR" as a password.

Gut bomb 
Enter "BRPS" as a password.

Full-time missiles 
Enter "Y_WNT_T" as a password to have unlimited missiles.
Note: "_" indicates a space. Then while playing a game, press Left to use the missiles.

Turbo mode 
Enter "CFFNYN" as a password.

Alternate textures 
Enter "JMPNG" as a password:
to change all textures in the game into pictures of one of the programmers of the game.

Change track color 
Enter "JMPR" as a password. Select "Done" and "JIM" will appear in the square. 
Press Start, select "New Game", then choose "Summit Rumble".
Select any number of players, but many CPU trucks. When the game begins,
there should be black squares with aliens or other objects in the middle.

Level passwords 
Level                      Password
Beginner

RuinsG[                   Up Arrow][Star]NJ2L0
Junk Yard                 J[Star]XQYN4G
The Heights                M[Star]OT1Q9R[Left Arrow]
Voodoo Island             P[Left Arrow]3W4TC[Star][Left Arrow]F[Up Arrow]
Greenhill Pass            5[Up Arrow]627WFX9[Left Arrow]23G
Wasteland                 V[Left Arrow]92[Up Arrow]2[Down Arrow]0CL56B5V
Aztec Valley              YYC5D2L3F[Right Arrow]89[Down Arrow]8[Right Arrow]B7
       
Intermediate

Ruins                     GBGJ5MTL
Junk Yard                 JNJMQL7S
The Heights               MJMPT[Right Arrow]XRN
Voodoo Island             PJPSWR0[Star]89R
Greenhill Pass            SBSV2[Star]3XBC[Up Arrow]4[Down Arrow]
Wasteland                 VBVY2X60[Down Arrow]FD7B2M
Aztec Valley              YFY15093H[Left Arrow]G[Up Arrow][Down Arrow]5675
Alpine Challenge          1N1483C6KLJDH89[Up Arrow]G4N
       
Expert

Ruins                     GKGH[Up Arrow]G[Star][Left Arrow]
Junk Yard                 JGJKLJP[Star]
The Heights               MSMN[Right Arrow]M7QW
Voodoo Island             PKPQRP[Up Arrow]T793
Greenhill Pass            SKST[Star]SDW[Up Arrow]C61R
Wasteland                 VOVWXVGZDF9463R
Aztec Valley              YGY209YJ2G[Left Arrow]C796462
Alpine Challenge          101231M5JLF[Up Arrow]C979S0D
Death Trap                404564P8M[Right Arrow][Left Arrow]DFC[Up Arrow]CV32KC