2carpros I have a hesitation or bucking problem when I accelerate

My car runs great most of the time but every now and then she hesitates seems like on every light throttle or when gunning it at lower speeds when I'm on 40mph or more she's never done it yet.I had the car for like 2weeks now when I first bought the car its never done it, but about a week ago it started, now I don't know if this has anything to do with it but I put a bottle of lucas fuel treatment in her about a week ago and that's when it seem to happen, some mechanics told me to change the fuel filter, air filter, 'check the plugs, I did all that I thought it worked but it did it again lastnite, I didn't change the plugs because they looked great the first plug was covered in oil I cleaned it up, I check it this morning and its still every clean. As far as the car goes she's a 5speed does not have a hard time starting, engine is super smooth don't even know she's on, another thing is that the weather out here has been changing one day its cold the next its hot or hot during the day cold at night, the reason why I mention this is because I had a 1990 Toyota pickup truck that did that something but in the winter she ran perfect or when it was raining outside, I spent tons of money on supposedly best mechanics and the problem was never solved I ended up sells her, I'm just scared that I'm going threw the same problem car with hesitation problems are hard to solve especially when it only does it everyonce and awhile, seems to never do it when I try to show the mechanics. Please help I will greatly appreciated it thank you