2001 Toyota Camry LE V4 Error Code p0401

 a 2001 Toyota Camry LE V4 with currently at 90K miles. The CEL light recently came up. When taken to an auto repair shop, they replaced the EGR valve saying the diaphragm was not opening when tested. But still the light is coming back on.

I tried to narrow down the error and found the following: -
1). As long as I am driving by accelerating slow and steady, the light doesn't come up.
2). When I try to push hard on accelerator while climbing up the slopes, the CEL is coming back on with EGR flow insufficient.

Also, for a 19 Gallon tank, the car is giving a total mileage of just 300-350 miles in city (if related to the same issue).

there are a few other possiblities that can cause this code to be set as well. EGR vsv (vacuum switching valve) EGR modulator or a mass air flow sensor that is not reading properly. i am not at work so i do not have the the flow chart at the moment but i do know that you will need access to a scanner that shows live data to be able to see what the sensors are doing. i can post the flow chat in the AM, or one of the other guys might be able to get that on here for you.