after checking the things that hondaman said, try hitting a steep hill, see if you can climb it, if it bogs still check your intake and exhaust for obstructions also b4 ripping the pump and filter out.
when my pump died it slowly stopped one day, it hung when going up a hill, then i couldnt go any faster than 40 day. And the next day i could barely move 20, ended replacing the whole gas tank b/c it rusted out clogged my filter and then burned out my pump.