I don't know that the valves will be out of spec, they sometimes never need any adjustment. But they should be checked just the same.
26,000 miles on factory spark plugs is a lot. These will show a lot of wear.
I would certainly arrange for a valve clearance check, install new spark plugs, test/adjust the Throttle Position Sensor, carefully inspect the throttle body boots for being loose and/or having slipped out of place ( common vacuum leak, which could cause your problems....), then do a proper throttle body synchronization.
Typically the TPS unit only acts up when engine is hot. While it cannot be ruled out, I doubt it is causing your issues.
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