I bought this car with barely 45,000 original miles on it in April of 2012. It now has 46,993 miles on it and it is hesitating some when taking off from a stop sign or a stop light. It idles fine but I can feel the steering wheel shaking just a tad at idle. Now, when I am just going a steady mileage (say 30-40 mph) sometimes it chugs, it doesn't surge, it kinda feels like it is losing power or missing and this is very sporadic. Also when it kicks down, or loses power, or chugs or whatever you want to call it I can hear what I think is a puffing noise from my tailpipe (I can slightly hear this from inside my car). In the last 4 months I have had a new smog pump put on it, a new water pump (the water pump wasn't bad but the pulley on it was growling so I replaced the whole thing), a new AC compressor, new plugs (AC Delco), new wires, cap, rotor, pcv valve, fuel filter and air filter. I can't find a dang mechanic to actually drive my car back and forth to work or drive it on a consistent basis to get it to act up and witness the symptoms and I don't know what to do next or what to even try and look for. I have been told it could be the fuel injectors, a bad catalytic converter, a vacuum leak and I'm sure I'm missing some other backyard mechanic diagnosis' lol. Also I had the full blown tune up done because it was doing this and it didn't solve the problem. What do you think?