2005 toyota matrix shutters and stalls after warming up

We have a 2005 toyota matrix with 152k miles. In the heat of the afternoon, or after driving 25-30 min the car begins to shutter. Slight hiccups when at speed, then stalls if idling, like at a stop light of the exit ramp. It starts right up, then dies when put in drive.
We have taken it to toyota, TWICE. On the second trip, the car died on them and they still found nothing. The check engine light is not on. There are no fault codes.
Toyota said replace the spark plugs, which I did. Still has same issue.
The ECM was replaced under warranty a couple years ago.

Really need to figure this out. Any thoughts will be appreciated.

The ECM was a known problem on these cars, but since you already replaced it.

The other known issue is a leaky intake manifold gasket, which can cause your symptoms without setting a code. My next step would be to replace the gasket. Toyota has a new thicker gasket, so make sure you get the new part #.

A bad vacuum leak would trigger a lean code.
I would suspect the crank & cam position sensors. One of them failing when hot.