It sounds like a case of low pressure from a failing pump or bad regulator. The constant need to prime as well as the poor acceleration are from it starving for fuel.
First check the fuel pump pressure itself. Connect a fuel pressure gauge to the line coming from the pump before the pressure regulator and see what it shows for pressure. (Should be around 30-40 psi minimum with the engine running at idle)
Test the regulator next, disconnect the vacuum line and see if there is any gas in the line ore coming out of the fitting. If yes the diaphragm has failed and you need a new regulator. If no gas in the line connect a pressure gauge inline between the regulator and the injectors and watch the fuel pressure as you remove the vacuum line. It should change if the regulator is working.
I think you will find low pressure, unfortunately the pump is in the tank. It is not that hard to change but it is not that fun. There should be a video or two online, but you did not state which model it is so I cannot link you to one.
Post back what you find after those tests and we can determine if it is the pump/regulator or something else.
Sunday, December 4th, 2016 AT 2:06 PM