Focus, 2001 Wagon SE 2.0 Zetec

My Focus wagon has just over 50k miles on it now and over it's life time is sometimes would surge just a little bit in the 45 - 50 speed
range. This has been going on for more than a year now but we don't put lots of miles on so maybe from 40k up.
Fuel filter has been replaced, some injector cleaner added. No help.
The surging has gotten quite bad, at first it was mostly at 35 -45 under minimal or no load but now I can detect it at highway speeds. At highway speed it feels like you're bucking a stiff gusty headwind. At the lower speed range it's just surging and I'm sure loss of power.
I don't detect or really know if this happens worse making right turns, I've read a lot about the fuel pump in the tank and it's possible cause of this. I do not have an error code or warning light. The engine starts and idles like a jewel.
Suggestings? I have a new set of plugs that I will install but I'm not thinking that it will fix it as I cannot detect a miss of any type, just surging..
I have searched this forum and all over the place but have not turned up much good info about this type of surging. Most of what I read is from people who have issues at starts and such.
Thank for any suggestions
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