I notice that sometimes when I press on the gas pedal there is a slight delay then all of a sudden there is the acceleration i was looking for

this usually happens when I am at very low speeds or even from a stop

I have changed the fuel filter about 20K ago
The fuel Pump around 30-40K ago
The air filter around 20-25K ago
The spark plugs around 30K ago (Bosch +4...could that be the problem?)
I use premium gas

any thing else it could be? Any suggestions?

thanks guys!