Hesitation in the engine

Well, a few months ago, I hit my exhaust tips on a curb while backing up. After that, I've had this skip in my engine, usually when I start off, and sometimes in the rest of the gears depending on how hard I try to push the gas in. When I hit the exhaust, all it did was bend some of the pipe, but I had that fixed. Since that time, I've replaced the primary O2 sensor, and I just replaced the timing belt today, but it still skips. I replaced the spark plugs and wires about two weeks before I hit the exhaust pipe. I even cleaned the fuel injectors. I only have a few options left on what it could be. I haven't changed the fuel filter in a while, so I'm going to do that very soon. Also, I think maybe the throttle position sensor might be bad. It might even be possible that one of the plugs might have fouled out too. Fuel pump maybe??? The engine isn't throwing any codes at all. Anybody ever had the same problem, or know what I might should check?