I have a 94' GMC Jimmy, and I believe I'm having problems with the fuel pump. It starts up just fine every time, but after driving it awhile it starts to act as if it's running out of gas. This happens especially on hills, and it will stall if I don't baby the gas pedal. I've replaced the fuel filter, and the fuel pressure is fluctuating between 45-55 psi. I think it's the fuel pump dying, my friend thinks it's the regulator, I've heard it could be the coil or a vacuum leak, is there any way to be certain? Sorry if this sounds like a dumb question, this is my first vehicle!