There could be so many things causing lag in a game.
Make sure you have GPUz running and get an idea of graphics card temps while playing.
Run HW Monitor to get CPU temps during a game.
Keep Task manager open in the background during a game so you can see whats happening to the CPU. Make sure nothing else is kicking off during the game.
Do you have a tool to check the wireless adapters lost packets? Run it during a game.
I recently had a similar problem and it turned out my wireless keyboard was too far from the USB transmitter in the case. I moved it closer and the lag vanished. Most of my lag related issues have been the various networking components (access points, noise, heat, etc.)
My first guess is to look at wireless issues. Can you switch your adapter for the wired one on the motherboard?
did it ever work right? If so, try to get back to that point and make changes one at a time until you can recreate it.