Big hesitation at 3000 RPM with 2001 XG

Recently my XG300 has started to have a very prolonged 'hesitation' @ 3000 rpm & above. It had been running perfectly & there are no stored codes. If
you drive it gently, you really think it's fine. But if you wind it up in the gears (autostick), it's got lots of go up to about 2800 rpm & then the rate of acceleration drops. It will still accelerate very slowly & unevenly & it doesn't matter what gear or if you are going uphill or not. I figured if it were a bad fuel filter (it's got about 60,000 mi) then it would show up more in the lower gears or going uphill, but not so. So now I wonder if there is an electronic high rev governor that has malfunctioned but doesn't show a code? Any ideas folks, this has me stumped & going to a dealer from where I live is a whole day's excursion. By the way everything else checks OK, plugs still look OK, starts easily & runs fine in D as long as you don't take it over say 2500 rpm.
BCinBC
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Sounds like it's likely a fuel pump issue, especially if it gets worse the longer you drive the car. A clogged catalytic converter causes a similar issue, but tends to be much less jerky than you describe.
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