Well if you threw a P0120, and have problems with pedal response, then you're next step should be to replace the TPS and see what happens. They're cheap and easy to get to.

Fuel filter, injectors, fuel pressure regulator should all be considered as well as the fuel pump. FPR's are cheap enough, but you have to take off the fuel rail to get to it so you might as well do both jobs at once, and fuel injectors are gonna run you $300+; so whether you attempt the pump second or last is up to you, dropping the tank is about the same amount of effort as removing the fuel rails. But you should start with a fuel filter cause it's easiest and cheapest.

Wouldn't hurt to poke the injectors with a multimeter or check for vacuum leaks either. Getting to injectors would cost you $20-50 in gaskets and checking for a vacuum leak just needs a can of brake clean and 2 minutes of your time.

I would doubt it's spark related if you're not misfiring and throwing a P0171. If anything you should see a P0172 or somethin that indicates it's too rich as fuel would be burning extremely unevenly.

Not too impressed by the mechanics response, but it is oddly in your best interest. If they don't have a clue you and would have to hunt gremlins it would cost you a small fortune. Still, these are all things he could've and should've advised you on.