Think back of all the times it has happen and what were the conditions like...for example was the outside temp cold or hot, full/low tank of gas, uphill/downhill, morning/afternoon/night, ect. Maybe your car is fine its just somthing else beside the components of your car cuase it drive bad.
I've heard stories of hard starts, low performance. They tried everything and couldn't figure it out, until the owner notice that it only happen with a full tank of gas. It ended up being everytime they filled up the gas tank it would expand and partialy squeeze the fuel line. well hope you find a common condition that will help you out.