I have a 1990 Toyota 4 Runner, with a replaced 1994 22RE 4 cyl. Running fine until a week ago. Slowly lost power over about a 5 mile span to the point it would not make it up a hill. Is greatly underpowered and intermittently cuts out nearly completely. Idles fine.

I thought fuel system. Replaced the fuel filter and plugs with no change. Never ran hot. Thinking fuel pump but it takes a special adapter apparently to measure the fuel pressure for the 90's models. Anyone have any ideas what this could be?