My 94 T100 4 cly acts like it's starving for fuel

Maybe something entirely different like an ignition problem. Describe the issue.

Bought the truck about a month ago. Drove great. About 2 weeks ago I put a bottle of fuel system cleaner and put in tank. A day or so later it started spitting and sputtering but not when pedal was to floor. I replaced fuel filter and didn't help or hurt. Two days later as I was driving it lost all power going up small hills. Then I noticed, while in neutral, I could put pedal to floor and engine would not rev. Made it home, but now it won't stay idling very long. When I mash throttle, it bogs down and cuts off.

If I clamp return hose it runs good.

Fuel pressure regulator?

I replaced the regulator, thought I had bought a bad regulator. So I took back and swapped out regulator, put it on and still same problem. I put a bottle of Seafoam in it yesterday and it's now running ?better? but still bogging down at times. It had sat for a little over a year before I bought truck.

Check the throttle position sensor. If you have a scan tool check and see if the level is going up and down when you press and depress the throttle.