Slow accleration, moderate jerking, noises

My car recently died and after having it towed to a mechanic shop, I found out that they had to replace the fuel pump. After receiving the car back, I have noticed that my car is a little sluggish at times, especially when the A/C is on.

The car will run really sluggish on acceleration, almost as if there is a major drop in power to the engine. It always spurts/jerks moderately around 2.5k-3k RPM. It also makes the knock around 3k+ and when I give it lots of gas, the car jerks more.

I have also noticed when I shift it into 5th gear (final gear) on the highway, the car won't want to accelerate much over 70mph and the RPM usually hangs around 1.5-2k.

I'm not sure if this is a simple spark plug issue or a clutch problem.