My exhaust got louder and my clutch feels like it's slipping.

[Resq]

Hello Zilvia I'm a new poster with limited experience in mechanics I bought my S13 out of pure love for the car scene. Recently I had my fuel pump, clutch, flywheel, headers gasket and tranny changed at once. After all this my car got louder for some reason. When I'm on a steady acceleration in 1st gear the car makes a popping noise like if it's struggling to push air out. It almost sounds like its backfiring. My clutch feels like it's slipping on idle my RPMs drop to almost 0, it doesn't idle over 1k. Also in neutral when moving the shift knob left and right it feels like it gets stuck moving it from the far left to the far right around the 5th/R gears. It also feels like I'm not pushing out the same amount of power I was before all this. Any ideas on what could be causing this? Also my exhaust is throwing a grayish smoke. Smells like burnt plastic.