No matter what speed I am going, the engine bogs if I step on the throttle medium to hard. Hesitates for a sec, then picks up.

No problem if I gently step on the gas.

I tested at the engine with the airbox off so it's not a clogged filter. I also changed plugs and shot some throttle body cleaner into the tb. No change.

ANY IDEAS?

I have 140k miles on mine. Around 100k, I had to replace the rear O2 sensor to turn get the "check engine" light to go off.
In the last few weeks I have noticed after I pull up to the first red light of the morning drive, when I try to take off, the engine almost dies. This lasts much more than one or two seconds and in fact I have almost been rear-ended more than once!
But it hasn't died yet. After several seconds of this, it finally takes off and I don't suffer this any more during the day. Even after 9 hours of sitting in the parking lot at work. Only when I first use the car in the day (usually this is the morning. But I have also used the car for the first time in the afternoon and it still hesitates. but not again until the next day.)
Minimal research I have done so far: the fuel filter is a usual suspect for this symptom but the Echo's filter is inside the gas tank, on top of the fuel pump. Don't know if there is an access hole in the bottom of the trunk to get to it or if the whole tank has to be dropped.
And if it is the fuel filter, wht does it only restrict fuel for the first drive of the day? Wy wouldn't it stay blocked all the time?
Anyway, that's my 2 cents worth.