hesitation/bog after shifts (automatic) Options

[krewzn_along]

I'm looking for experience to solve this problem, really an annoyance. Ideas of what it 'could' be I've got but haven't found anything to solve this yet.

Accelerating wide open or hard throttle there is a power gap, lag, hesitation, bog, just after gear shifts. It's an automatic. It's noticable at the shift to 2 and 3, where you have the power on full. It just lasts for probably less than a second and then the engine is back full power. If you accelerate at partial or moderate full throttle it does not happen.

This has been going on for a while, maybe a year - it didn't start all of a sudden. Recent maintenance includes plugs, spark wires, rotor & cap, checked the intake path and found/fixed break in hose after the air cleaner, all the hoses look/feel good, and it otherwise runs great.

Seems like maybe an ignition timing or vacuum/controls thing since it happens just after the engine's made a change in revs and manifold pressure and timing have changed/are changing. But I haven't found anything wrong.

'97 ST204 (way cool I figured that outm huh? ) at 140k mi. Timing belt's been done.
2nd Owner - well taken care of, probably driven a bit hard by my 20 yo daughter.

As for things that need attention, valve guides are probably worn as seen by smoke on start-up (wouldn't cause this problem), and I'm wondering if the valves need adjusting as the top of the engine seems noisy to me (I've had a few toyotas so I know they are often a bit noisy around the valves).

Anyone had anything like this and figured it out?

TIA,