High end PC having big FPS drops?

Hello there FP peoples.

So a while back I completely upgraded my PC and built my own high end PC with the following parts:
Fractal Design Define R5 w/Window (Titanium) ATX Mid Tower Case
Intel Core i7-5960X 3.0GHz 8-Core Processor
Corsair H100i Liquid CPU Cooler
Asus X99-DELUXE ATX Motherboard
Corsair Dominator Platinum 32GB DDR4-2666 Memory
Samsung 850 EVO-Series 500GB 2.5" Solid State Drive
Western Digital Caviar Black 1TB 3.5" 7200RPM Internal Hard Drive
Corsair RM 1000W 80+ Gold Certified Fully-Modular ATX Power Supply
Dual GeForce® G​TX™ 980 Ti graphics cards (2-way SLI)
EVGA Pro SLI Bridge V2

I decided to play some GMod today and I noticed I would have massive random frame drops… I disabled SLI and I still had the same problem. A PC with those specs shouldn’t really lag in a game like GMod so does anyone know whats up?

Some Garry’s Mod maps/entities are un-optimized crap. While not a 2-way SLI 980Ti, my 670 has the same issues, which again, Shouldn’t be possible but just is.

I just don’t get it though. Other players seem to be having no problems what so ever.

I guess it’s random, my 550Ti honestly ran Gmod better than my 670 is.