2011 Aveo LT Intermittent acceleration problem

Hey everyone this is my first time posting on here. I need help please! 2011 Aveo LT has a problem with accelerating, like merging onto a highway, it does not want to go. It just puts along as if I'm not flooring it! It seems sometimes if I take my foot off the gas and then back on the engine seems to "catch" and will accelerate how it should. I gave it to one of the best mechanics I know for almost a month and the problem only happened 1 time! The scanner was ran on it, everything tested fine. It just happens out of the blue. I've tried to see when it happens, how much fuel is in the tank, time of day or temperature outside, engine temp, anything I can think of that would help me figure this out. The original plugs were in it so I replaced those and drove it for a while, it still happened eventually. I unplugged the MAF sensor to see if there was a change while the vehicle was running but that came out fine as did electronically testing it. Cat is no clogged either. Idk if this has anything to do with it but I was told by someone that if there was a slight coolant leak over time, the head gasket could be bad. Even if the car never over heated, just had to add a little bit of coolant every couple months. He said that was what happened with his Volvo. I did have a small leak where the coolant temp sensor goes in so I fixed that a few months ago. I'm gonna do a test on the head gasket to see. Does anyone have anything that would help me?? Reslly stuck and this is a dangerous situation when trying to merge in a highway and the car just puts along. Can not afford a new car right now. And chevy doesnt know what's wrong of course. I was thinking it could be the accelerator pedal position sensor attached to the gas pedal but I dont just want to throw parts at it. Someone help!! Email me please ndimatties@gmail.com thank you so much!