[V8] loss of power/surging

[aukdav]

Just came upon a new purchase a week ago and am trying to iron out some problems.  I checked the archives and found some suggestions, followed them, and still have the same problem.

Car surges slightly on constant and partial accel.  WOT, the car pulls like a train.

Per archives, I've replaced the 02 sensor will a generic Bosch 3-wire sensor.  Problem persists.  Checked the #5 fuse and it was fine, but replaced just in case.  I next replaced the fuel filter with new factory filter.  Problem seems to have worsened.  Now the car has a big stumble when first accelerating.  Almost a complete loss of power.  It will eventually recover and not resurface, but the surging remains.  Again, WOT is fine.

What is the next step?

Thanks,
Dave