This mod will improve & fix various vehicle related things in Grand Theft Auto V. I highly recommend using Law Enforcement Improvements by Custo, Unmutual, Netman and Olanov alongside this mod, with my popgroups.ymt and vehicles.meta.
IMPROVEMENTS/TWEAKS:
Vehiclemodelsets.meta-Lost MC use the Slamvan2 alongside the Gang Burrito & Hexer. FIB vehicles spawn near the dishes in Sandy Shores.
The Post-OP Boxville can now be seen pulling out of driveways during the "DELIVERY" scenario, along with the Deludamol Rumpo and Bugstars Burrito.
The Monroe, Z-Type, B-Type and Kalahari spawn parked in the Vineyard parking lot randomly.
The BF Bifta can be seen driving along dirt roads in Blaine County randomly.
Textures - Emperor, Manana, Romero, Slamvan2 now have whitewalls on the stock wheels. Rhapsody has black wall tires on the stock wheels.
Popgroups.ymt (stock 360 .meta converted to .ymt with Notepad, all respective DLC vehicles added to their respective groups)-Kuruma (no not the armored one), Buffalo S, Blade, Intruder, Asea, Premier, Primo, Sultan, Minivan added to the VEH_MID group - they'll now spawn in middle class areas (the Primo, Asea, Premier, Minivan and Sultan were originally only in VEH_POOR-the Blade never spawned stock).
Elegy, Tailgater, Vacca, Cogcabrio and Coquette Classic added to the VEH_RICH group - they'll now spawn in rich areas.
Also moved the Baller, Baller2, Dubsta, Pigalle and Huntley to the Rich group. The Karin Beejay XL has been moved to the VEH_MID group.
The Enduro, Slamvan, both Ratloaders, Rancher XL, Duneloader and Bobcat XL have been added to the VEH_SALT group - they'll now spawn driving around Sandy Shores.
Added the Bison, Sadler, Bobcat XL and Trashmaster to the LARGE_CITY group - you can now see them randomly driving around Los Santos.
The Voodoo2, Surfer and Surfer2 have been added to VEH_POOR - you can now see them driving around the poor areas of Los Santos.
FIXES:
Vehicles.meta-removed SMALL_WORKER flag from vans (Speedo, Rumpo, Burrito). This flag was broken and was stopping them from spawning in traffic.
Vehicles.meta (mpchristmas2)-Added flags for the Slamvan allowing it to spawn in traffic.
carvariations.meta(spupgrade) - Fixed the Dukes and Stallion spawning with "SA EXEMPT" plates.
Textures - Fixed Rumpo not spawning with the blank livery.

UPDATE:June 10th
-Virgo spawns in traffic
-Stirling GT spawns parked in the Vineyard parking lot, along with the Stinger, Stinger GT and Entity XF.
-Virgo has white walls on stock wheels.

UPDATE:June 12th
-Rusty and clean Karin Rebel added to VEH_POOR in popgroups.ymt - they'll now spawn in the rougher areas of Los Santos.

UPDATE:June 15th
-Moved Kuruma to VEH_RICH
-Coquette Classic now only spawns parked at the Vineyard
-Flatbed added to LARGE_CITY group

UPDATE: June 21st
-Removed POOR_CAR flag from Sultan in vehicles.meta
-Removed Sultan from VEH_POOR group in popgroups.ymt
-Optional .ini for use with PlasticTangerine's "Create Your Own Natural Vehicle Spawns" included
-Changed AVERAGE_CAR flag on Elegy to RICH_CAR
-Added Bifta, Kalahari and Paradise to BEACH_PARTY group in vehiclemodelsets.meta, they can now be seen parked near/on some beaches late at night

UPDATE:June 27th
-Changed Kuruma's VEH_AVERAGE flag to VEH_RICH in the mpheist vehicles.meta, also changed SWANKNESS_LEVEL from 2 to 5
-Pics for locations of vehicles in .ini for use with PlasticTangerine's "Create Your Own Natural Vehicle Spawns" now included

UPDATE:July 1st
-Fixed a colossal amount of vehicles only spawning parked in certain colors and not spawning driving with them - this had to do with the "MaxNum" line in vehicles.meta
The following vehicles were affected:
F620
Exemplar
Blade
Blista Compact (Blista2)
Banshee
Mixer
Mixer2
Super Diamond
Rapid GT hardtop and soft-top
Surano
Bullet GT
Vacca
Rhapsody
Pigalle
Dukes
Stallion
Warrener
Furore GT
Emperor (Rusty)
Surfer (Rusty)
Towtruck (Slamvan based)
Journey
Alpha
Jester
Massacro
Dominator
Gauntlet
Sandking SWB
Sandking XL
Hakuchou
Thrust

UPDATE:July 2nd
-Revised description
-Few small revisions of the "MaxNum" line for a few vehicles in vehicles.meta.

UPDATE:July 4th
-Changed frequency and maxnum on the Kuruma (mpheist vehicles.meta) and Jester (mpbusiness vehicles.meta)
-Added FLAG_SPORTS flag to the Kuruma
-All traffic is now Liberators, Sandking SWBs and Sandking XLs. Just kidding!

UPDATE:July 6th
-Further adjusted the Jester's frequency & maxnum lines in the mpbusiness vehicles.meta file
-Removed the "DONT_SPAWN_IN_CARGEN" flag from the BF Surfer (base game vehicles.meta)

UPDATE:July 8th
-Chino spawns in traffic
-Speeder and Toro spawn at the purchaseable marina
-Brawler spawns at the start of 2 of the 4x4 races
Once the .asi stuff gets patched for the current game version, i'll most likely include parked spawns for the Progen T20 and Coquette3/Coquette BlackFin in the .ini for use with PlasticTangerine's "Create Your Own Natural Vehicle Spawns"

UPDATE:July 9th
-Brawler added to .ini
I'd add the Coquette Blackfin and T20, but alas, PlasticTangerine won't update the "Create Your Own Natural Vehicle spawns" mod and put more than 15 slots.

UPDATE:July 10th
-Innovation added to BIKER_GANG group in vehiclemodelsets.meta, meaning you can now see the Lost MC riding the Innovation.

UPDATE:October 8th
-Most likely the final update, fixed the Rental Bus and utility version of the Boxville only having 1 of 2 of their liveries.

UPDATE:October 20th
-Added Faction, Moonbeam and clean Voodoo to traffic.
(removed due to lack of car color lines)

UPDATE:December 15th
-Added Cognoscenti, Cog55, Tampa, Schafter3 and Schafter4 to traffic.

UPDATE:December 16th
-Removed the Cognoscenti, Cog55, Schafter3 and Schafter4 from traffic due to lack of car color lines - they only spawned in black with maroon accented interiors.

UPDATE:December 18th
-Readded the Cognoscenti, Cog55, Schafter3 and Schafter4 to traffic. Thanks to TheAdmiester for making them spawn with multiple carcols by editing the mpapartment carvariations.meta

UPDATE:March 12th 2016
-Mod now includes GLion's "More color variation for DLC cars" mod, big thanks goes to him for letting me include it.
-Readded the Voodoo, Faction and Moonbeam to traffic

UPDATE:March 18th 2016
-Virgo3 (stock IV Virgo) added to traffic
-Newest version of GLion's color mod included
-Updated IVPack compatible popgroups

UPDATE:March 23rd 2016
-Updated IVPack compatible popgroups