Poor acceleration

i Have a 2004 hyundai sonata, with aprox. 60,000 miles on it, and i have been having some issues with the car. it seems to stutter (it feels like a stall) a lot whenever i try to accelerate, especially in cold or rainy weather. after some time the stuttering does stop but i need to know what the root of the issue is. i have already tried changing the air filter, and adding fuel injector cleaner, but that didn't seem to help at all. the car also has a sqeaky belt and i am wondering if this could be part of the problem, or something more superficial. any information you have would be greatly appreciated.