When I step on the gas sometimes the vehicle just chugs along like it is not getting gas or air or something it needs. The older the vehicle gets, the worse it gets. Help!!!!!!!

I don't know if this is related to the rattle. That started early on, but now the car chugs! GRRRR! Scarey! SO fun when you pullout on the interstate much less at a stop light turning or even just trying to accelerate. Took it to the dealer. Asked them to check it -no response.