Where is the fuel tank pressure sensor located?

The pressure sensor is mounted to the top of the fuel pump module in the top of the tank. To access it you normally need to drop the tank. Unless you have very small hands and can reach up on top of the tank to get to the pump.
Why do you think the sensor is bad? It's not a common failure item. Are you getting an EVAP code or is live data not showing a pressure change from the sensor?

Pressure sensor in the tank won't cause that. Its only real job is to tell the ECM if the EVAP system is working as it should. Basically, during an EVAP system test the engine running the tank vent valve closes, the purge solenoid opens, and it pulls a partial vacuum on the tank. The pressure sensor on the tank tells the ECM that "Yes I see a partial vacuum of X" Once that number hits a certain point the purge solenoid closes, and it holds the vacuum amount. The pressure sensor says that "The level is holding or degrading at this rate" It holds that for a set time and then opens the vent valve and the vacuum drops back to atmospheric pressure. During all of this the ECU is looking at tables telling it the numbers it should see for each step and if anything is wrong you get certain codes, for instance a code P0440 which indicates a large EVAP leak.
In your case I suspect the issue is actually a bad purge valve. The common symptom is that you fill the car with fuel, and it will either not start up easily when you hit the key (but will start if you crank it long enough) or it will start run a couple seconds and shut off. It will do it again when filled the next time as well. It will be intermittent until the valve finally fails open and stays there. Basically the issue is that the valve stays open and as you fill the tank the fuel vapors need a place to go, normally they would be trapped in the charcoal canister, but with the valve open they will flood into the engine intake manifold and act like you dumped a lot of fuel in the engine, just like an older engine with a choke stuck on. The mix is so rich it cannot ignite until enough air is drawn in to lean it out.

As such I would check the purge valve first. It's a common failure item on GM engines (and many others). It is located on the intake manifold next to the throttle body and requires you to first find it, then remove the EVAP lines using the quick disconnect fittings and the electrical connector. Then remove the bolt that holds it. Reverse the process to install its replacement. The bolt gets snugged down and the lines and electrical connector are re-attached. This is the same repair and an explanation of the issue that one stuck fully open will do, yours may not be stuck full open. Note the discussion of the pressure sensor.

https://www.youtube.com/watch?v=PjuJNR9cyzg