Q: After major engine work, car's response is slower. Having to push the pedal harder then usual. Seems like torque or power loss.

My timing chain snaped while driving. Luckily i was only going 10mph but the damage was done. 4 valves were bent and damaged the cylinder head. Went to my local mechanic who replaced the valves brand new BUT he sent the head to a shop where I guess they refurbish it? Also he replaced water pump, chain, pullies, tensioner spark plugs etc. After a month, I received my car back and immediately noticed it doesn't respond the same. I put those chemicals in the gas tank where they clean the fuel injectors etc. It helped but didn't fix the problem. After confronting him about it, he prides himself saying he did the job very carefully and accurately. Could this be permanent power loss sense he re-used the same head? Do I have to get a new engine or is this recoverable? No engine codes are on when I checked for them. Lets say your accelerating and take your foot off the pedal and feel that jerk of deceleration. Thats the feeling I'm getting when first taking off without removing my any pressure

My car has 96350 miles.
My car has an automatic transmission.