I am continuing to try and diagnose the severe bucking problem between 1,500 and 4,000 PRM under load.

The fuel pressure at the rail is 38-40 PSI. It should be 43.5. So when I went to do a volume test at the return line, nothing came out (since the FPR does not divert till the pressure reaches 43.5)

I turned off the fuel pump and a few minutes later, the pressure creeps up to 42-43 and a few drops of fuel comes out of the FPR return line.
So I am guessing that my problem is fuel pressure, but before I buy a $300 pump (1995 T has a single intank pump), I want to be sure it is not something else. I replaced the filter earlier in my saga. But would the rise in pressure after the pump is off indicate that the filter or something else is blocking the line (and fuel is seeping through over time). Or should I buy yet another part that I am "sure" must be the problem?