'97 Sunfire Bogs Down When Shifting

[97sunfire2.4vert]

I bought a '97 sunfire convertible with the 2.4l in it about 6 months ago with 97k on it and have put a little over 9k miles on it since then with almost no issues(mostly highway miles, I have a 50 mile commute). But it started bogging down sometimes when I shifted down to 2nd through a turn and accelerated out out of the turn (not talking speed racer here). this started to happen when I shifted up a gear as well (not any particular gear) and it started grinding occasionally when I shifted down into 2nd. at this point I got an oil change (it had been 3k mile) and took it to a mechanic who "couldn't duplicate my problem", my guess was that when they topped off my fluids when i got the oil changed it eliminated the problem. but on the way home from the mechanic it bogged down ever so slightly once and started to increase in frequency again but didn't start grinding again until recently. also for some reason it only happens once it warms up, it will never happen right away. the only leaks I am aware of on the car is a slight coolant leak and she uses a little oil (about a quart low after 3k miles). what is really confusing is the me is the fact that it is sparatic about whether or not it does it, sometimes i can drive 50 mile and have no issues and other times it just has to warm up and I'm having trouble shifting like an inteligent person. I have been keeping up to date on my oil changes as well but the last one I didn't get the fluids topped off, but I'm about to change the oil again so I'll check the fluids then. I was thinking O2 sensor or maybe fuel filter because it seems like a lack of fuel flow not something in the tranny but am unsure which to do (I don'y have a lot of extra $ to do experimental repairs). Oh one last thing, when I had the mechanic check it out he checked the misfire counter and it was at zero so spark plugs don't seem to be the issue. But I am far from an expert on the subject lol.
Sorry that took so long and THANK YOU SO MUCH to whoever helps!

 

[melsg5]

change the fuel filter and air filter, if it hasnt been done. Check for a fluid leak at the clutch master or slave cylinder.

 

[2000SunfireGT]

change the fuel filter and air filter, if it hasnt been done.

if the air or fuel filter is clogged your car will act like this. it could also very well be the throttle position sensor. is there a check engine light on?