Help! 96 tacoma 2.7 running issues

My 96 2.7 5 speed manual starts right up and idles very smoothly when in neutral you can rev it up and it revs like it should. The problem that I am having is when I try to accelerate the truck stumbles and if I hold my foot steady on the accelerator pedal the stumbling stops and it acts like the fuel is shut off then starts stumbling again. So far I have changed the fuel filter, air filter, vacuum lines, PCV valve, Distributer cap and rotor button and coil, also checked for excessive free play in they distributer and it was fine, had the timing checked, had the cat checked, checked and cleaned the MAF, had codes checked the only one I had was a P0171. Does anyone know what may be going on with it or have a similar issue? Was told it could either be a TPS or Fuel pump

 

You need to check fuel pressure next. Somewhere on fuel rail should be port but I am not for sure. P0171 system lean so check for vacuum leaks too.