The Bravado Buffalo STX from the The Contract update with ALL tuning parts included and fully usable, along with a moving & tunable steering wheel, shaking engine block & exhaust, AO and all liveries.
I've included the .max project file for anyone who wants to make their own fully tunable car.

The car is FULLY stable with 77 tuning parts, it can be shot, spawned 10+ times, thrown into dynamic objects or exploded without the game crashing.

PUT BUFFALO4.DAT INTO THE "carmods" FOLDER! (if it doesn't exist, create a folder called "carmods" in your game folder and put the .dat there)
CAR REQUIRES THIS TRAINER 21.09.26.1 AND UP TO WORK PROPERLY https://gtaforums.com/topic/896795-1000-1080-zolika1351s-trainermod-menu-rewritten/

Use https://gtaforums.com/topic/955449-iv-zolikapatch/ to make the steering wheel move and engine & exhaust shake

Note that because of the high amount of tuning parts, this car might cause performance issues on low-end systems.

Vehicles.ide:
buffalo4, buffalo4, car, BUFFALO3, BUFFALO, VEH@STD, NULL, 50, 999, 0.2974, 0.2974, 0, 5, 1.0 ,0 livery+wheelangle:-19.8875
txdp
vehshareVdirt, vehshare
muscle_supercharger, vehshareVdirt
muscle_n_w_interior, muscle_supercharger
buffalo4, muscle_n_w_interior

Handling.dat:
BUFFALO3 1700.0 7.5 85 0.0 0.0 -0.24 0.0 5 0.23 1.0 155.0 0.25 0.65 0.7 35.0 1.35 1.10 13.5 0.15 0.48 2.0 1.2 1.2 0.13 -0.13 0.0 0.5 1.0 1.0 0.8 1.5 0.0 25000 440010 1 0

Carcols.dat:
buffalo4, 0,0,3, 0,0,103, 3,3,103, 1,1,79, 3,3,73, 4,4,82, 6,6,84, 11,11,86, 16,16,92, 23,23,25, 34,34,28, 36,36,27, 47,47,91, 52,52,53, 53,53,51, 64,64,65, 69,69,63, 70,70,64, 73,73,58, 76,76,58, 2,2,63, 21,21,72, 22,22,72, 13,11,91, 19,19,93,

Tuning part count: 77
Tuning part list:
Roll Cage
Padded Cage w/ Carbon Seats
Padded Cage w/ Seats
Padded Cage w/ Race Seats
Padded Cage w/ Street Seats
Padded Cage w/ Tuner Seats
Angled Exhausts
Single Angled Exhaust
Medium Bore Exhausts
Single Medium Bore Exhaust
Big Bore Exhausts
Single Big Bore Exhaust
Chrome Side Exit Exhausts
Titanium Side Exit Exhaust
Vent Delete Hood
Front Facing Vent Hood
Muscle Car Hood
Recessed Hood
Custom Intercooler
Intercooler w/ Pump
Intercooler w/ Small Logo
Intercooler w/ Large Logo
Intercooler w/ Twin Fans
Custom Louvers
Angled Louvers
Race Scoop
Secondary Race Scoop
Tuner Scoop
Secondary Tuner Scoop
Competition Scoop
Competition Scoop Alt
Carbon Vortex Gen
Double Vortex Gen
Carbon Double Vortex Gen
Roof Fin
Carbon Roof Fin
Double Roof Fin
Carbon Double Roof Fin
Race Skirt
Secondary Race Skirt
Street Skirt
Secondary Street Skirt
Custom Splitter
Secondary Custom Splitter
Race Splitter
Secondary Race Splitter
Street Splitter
Secondary Street Splitter
Competition Splitter
Secondary Competition Splitter
Plastic Sunstrip
Primary Sunstrip
Small Lip Spoiler
Secondary Small Lip Spoiler
Medium Lip Spoiler
Secondary Medium Lip Spoiler
Cut Lip Spoiler
Secondary Cut Lip Spoiler
Small Wing
Race Wing
Tuner Wing
Street Wing
Medium Wing
Angled Wing
Big Wing
Chassis Mounted Wing
Alt Chassis Mounted Wing