I had this problem too, Toyota was not able to diagnose it.
I changed plugs, higher octane, lower octane, Air Filter
, cleaned the throttle body too. Nothing made a difference.
I found it was kinda "bottoming out" when I first put some gas to it, like it would pause before it gave me anything.
This started happening shortly after my wife took my car to Crappy Tire for an oil change (she now knows this is a bad thing) and they cross threaded my oil plug and it was leaking all over the place.
I don't know if it was related or not (maybe the oil pump??) since my engine has now blown.