Suggestions on "Stumbling or Bogging" issue with 2.7

1999 Prerunner, 137k miles, automatic, no mods. Has a stumble or bogging feeling between 2k and 3k rpm. Was like that when I got it. It idles perfectly. NO Codes ever.

I have replaced plugs and fuel filter but no help....can you guide me to the next logical thing to check? This morning, I cleaned the Throttle Body and replaced the plug wires....no improvement.

It stumbles or bogs around the shift points mainly, it seems. A friend suggested it might be associated with a transmission solenoid, but seems like a fuel issue to me.

I even had the Toyota Stealership "Diagnose" it. All they could come up with is their High Revenue $289 "Throttle Body and Fuel Injector Cleaning".

Don't want to just throw more parts at it.

Tks in advance!

 

Today, I took it on the highway and it ran rough thru all gears and rpms. I got home, put it in park and ran the rpms up over 4k ....SMOOTH AS SILK.