Whenever I'm exploring in the game and fighting minor enemies such as mantis the game runs well but when I started fighting the Powder Gangers during the GoodSprings my game just drops in frames.Even if I manage to kill them the game stays in "slow motion". I'm currently using the 4gb patcher. http://www.nexusmods.com/newvegas/mods/62552/?
I've unistalled mods that I thought would impacted it such as IMPACT or EXE but still nothing.

Load order:
FalloutNV.esm=1
TribalPack.esm=1
MercenaryPack.esm=1
ClassicPack.esm=1
CaravanPack.esm=1
DeadMoney.esm=1
HonestHearts.esm=1
OldWorldBlues.esm=1
LonesomeRoad.esm=1
GunRunnersArsenal.esm=1
More Perks.esm=1
More Traits.esm=1
OONV.esm=1
FCOMaster.esm=1
GreatKhanGreatOverhaul.esm=1
DragsVGUArmorBase.esm=1
CFWNV.esm=1
Project Nevada - Core.esm=1
Project Nevada - Cyberware.esp=1
Project Nevada - Equipment.esm=1
AnimationProject.esm=1
Weapons.of.the.New.Millenia.esm=1
The Mod Configuration Menu.esp=1
The Weapon Mod Menu.esp=1
Vurt's WFO.esp=1
Conelrad 640-1240.esp=1
OldWorldRadio.esp=1
Readius_NV.esp=1
EVE FNV - ALL DLC.esp=1
dD - Enhanced Blood Main NV.esp=1
GasPumpsOfNV.esp=1
NCR Rearmed.esp=1
CCSP2_5d.esp=1
FOVSlider.esp=1
More Perks Update.esp=1
More Traits Update.esp=1
New Vegas Essentials.esp=1
OONV - Override.esp=1
B42 RWMS.esp=1
FCO - NPC Changes.esp=1
FCO - GlowingOne.esp=0
FCO - OHSB NPC Edits.esp=1
FCO - Russell.esp=0
ELECTRO-CITY - Imaginator.esp=1
Witcher Style Rifle Holster.esp=1
TheLozza's_Gasmasks_V2.esp=1
NCR Overwatch Armor V2.esp=1
Ranger Merc Helms - Helmet Hunt.esp=1
1nivVSLArmors.esp=1
Tribal T-51b Helmet.esp=1
Wanderers_Leather.esp=1
WastelandLootersNV.esp=1
Vagrant Armor.esp=1
hz_1 by 1 Reload Fix.esp=1
lexx_rifleholster.esp=1
GlovesGalore_DeadMoney.esp=1
GlovesGalore.esp=1
PowerArmorSize.esp=1
FO4-FNVPorts.esp=1
FO4PowerArmorReplacersNoDLC.esp=1
FO4PowerArmorReplacersWithDLC.esp=1
PublicPack4.esp=1
TheLegionWillRyse.esp=1
NCROverhaul.esp=1
FNV Realistic Wasteland Lighting - Full.esp=1
nukas.esp=1
SimpleCassReplacer.esp=1
ScavengerRadiationSuit.esp=1
UpgradesFromTheCommonwealth.esp=1
TacticalMarlin1894.esp=1
AK_AR15WP.esp=1
CFW-DLC.esp=1
MCL_Weapon_Pack.esp=1
PaintYourWeapon.esp=1
Decer_STALKER_WP_v1.1.esp=1
Decer_STALKER_WP_CALIBER.esp=0
Decer_STALKER_WP_SOUND.esp=1
BT87.esp=1
BHPM1935.esp=1
CFA_ClassicG11.esp=1
Classic10mmPistol.esp=1
Classic10mmSMG.esp=1
Colt_Monitor_R80.esp=1
Colt N99 10mm.esp=1
FAMAS.esp=1
Galil.esp=1
M1903A3Springfield.esp=1
R700.esp=1
Ruger Mini-14 Ver1.0.esp=1
TOZ66.esp=1
GaussPistol.esp=1
Vz61 Ver1.1.esp=1
M1897.esp=1
S16.esp=1
GRA-WRP-Patch-Two_Unofficial.esp=1
Project Nevada - Dead Money.esp=1
Project Nevada - Honest Hearts.esp=1
Project Nevada - Old World Blues.esp=1
Project Nevada - Lonesome Road.esp=1
Project Nevada - Gun Runners' Arsenal.esp=1
Project Nevada - EVE All DLC.esp=1
AmmoChecking.esp=1
IronSightsFoley.esp=1
ItemBrowser.esp=1
M-1 Carbine.esp=1
Weapons.of.the.New.Millenia.Cheat.Cabinet.esp=1
Weapons.of.the.New.Millenia.Leveled.Lists.esp=1
AUGA1.esp=1
Reload Sounds.esp=1
WeaponAnimations.esp=1
L96.esp=1
HZSmoothLight.esp=1
Door!.esp=1
Zan_AutoPurge_SmartAgro_NV.esp=1
Couriers Blunder + Rifle.esp=1

It might be worth disabling ALL mods and testing your game after activating them in small groups, maybe do it in 5s so it's less tedious

It's difficult to pinpoint any one mod with as many as you have running there.

I can't help but noticing though that you have both FO4 power armor plugins from dragbody ticked... you only really need one or the other. It'd also be smarter to use the PN merged DLC plugin as opposed to all of them individually. That FNV realistic lighting plugin should be down at the bottom of your load order as well... Your load order could definitely benefit from a bit of spring cleaning. Now, I'm not saying that's what causing your issue, it's likely a singly plugin, but a sort through couldn't hurt.

You do have a lot of mods. If one effects the muzzleflash, it could be that. Also any weapons that are 4k might do it. If you have a good computer, it wont be too much of a problem. I would suggest the "better casing performance" mod on the nexus. It has helped my performance in combat.

Depending on how picky you are about immersion, you could use a mod to remove muzzle flash, because it could be that as well. those are some of my suggestions. I hope this helps and I understand how annoying it is when NV slows down.

Cheers