1. Components.xml. Set mover sim standing height to 4444 0 4444. You can use higher or lower values but the higher the easier to lose control and the lower the less effective on NPCS. This height makes you and the NPCS very tall and when you attack the zombies with dynamites or fire bottles they'll fly away. Also explosive rifle (NOT DIRECTLY) works well. This height also prevents you from drowning in water. And finally it helps you move around with "poltergeist" aka motion antifreeze regardless the map height, because you won't get stuck below the map, when you spawn you'll automatically get teleported to ground level. Obviously if you spawn in the air you'll need to kill yourself after cleaning if you can't spawn a mount or use one nearby. Avoid trees BY ALL MEANS or you'll get ejected to the sky with no control in a ragdoll effect. The only ways to get out of it is either restart the game or turn invincibility off until you hit something and die, or if there's not much lag/zombies you can go to a private session or the outfitter and back. If you switch sessions while in the ragdoll effect you'll probably end up in a neverending loading screen.
2. gent.xml. Use high speed walking and when you walk use fists cover, it helps keep control when you bumb into things. If a tree or railway pushes you up to the sky, keep holding L2 and R1 (fists) till you go back to the ground.
3. gped.xml. Use y=1.5 offset so you can see the NPCS when you come back from antifreeze. Otherwise you will see the blurred map layer but not the bodies, especially in Armadillo. If you are able to see the bodies before the whole map loads you'll be able to find them and engage them.
4. Use full session freeze wagons all the time. Unpopular as it might by amongst legits, it's the only way to clean lobbies. Focus on freezing rather than on fully fixing an empty session. Once empty, switch even if it's infected, you can always fully disinfect the next one. It is extremely important because there's a lot of session-jumpers and all they do is worsen things, so freeze them asap.
5. This is a team work, you're not gonna achieve anything on your own unless there's PSN problems for everyone or very few people online. So if you get together with 6 or 7 people and each go for one lobby it's obviously more efficient. Also you should switch between normal, friendly and hardcore all the time
6. You'll need the cheat menu. I recommend turning on only the cheats you're gonna work with to save time and make your work more efficient. Invincibility, infinite dead eye, infinite ammo, donkey/horse, wagons, clear bounty, diplomatic immunity, dead eye level 1.
7. You'll be able to kill the standing NPC's with any gun, including revolvers. The ones lying down can only be killed with the effect of an explosion - be it dynamite, a fire bottle directly on them or an explosive rifle shot. Important, do not shoot them with ER directly, shoot to to ground around them or the walls/roofs. If you shoot them they won't go, if you shoot around them they'll be gone.
8. There's usually lot's of leechers/xp boosters in McFarlane's especially in friendly mode. The mods works best if you attack NPCs that are not close to other players so make sure there's no other players close to you and if so attack the NPC's on the other end.
9. The most effective guns against NPC's are dynamites and explosive rifle. If you're gonna use dynamite I recommend turning on dead eye level 1 and then do the rapid fire glitch so you can throw a lot of dynamites quick. Dynamite works best in the short range. Explosive rifle is good to reach NPC's that are not near.
10. A good technique to attack either McFarlane's or Armadillo is to go to a high spot and poltergeist/antifreeze from there, then spawn in the sky above the town. You'll see most bodies an they'll be within range.
11. A session is not clean until regular NPCS (horses, ranchers) start spawning and not even that, sometimes there's 1 or 2 bodies around so make sure you keep seeking and removing them. Also you'll need to check both Armadillo and McFarlane's.
12. You need a lot of patience. Sometimes you will have cleaned a session and suddenly a noob joins and brings 50 bodies with him. Well, you have the tools to quickly change that and you can freeze him.
In the end, this is just a working method that can fix and has previously fixed Red Dead, but again it depends on players. Rockstar is never going to release a title update for a 6 year old game worth maybe 4% of their total sales. Most people that broke the game in the past have matured but there's always lost bullets willing to have their moment of disgrace breaking the master piece Red Dead is.