HI new to the site,

I just bought a 99 cobra svt and love it!! but every once in a while it starts acting up,it seems to start acting up after I'v been driving for a while and the last two time's was when it got to a quarter tank of gas and was fine when filled it up. What its doing is hesitating and jerking like its running out of gas only when on the throttle around 2500 and higher rpms. Im thinking the fuel pump might be going out its not throwing any codes, another thing I was wondering if I replace the fuel pump can I upgrade even know Im all stock?