Skip the first few paragraphs if you don't care about what leads up to my question (which is posted at the end of this thread)

Keep in mind I could have installed this thing incorrectly.
(I borrowed the parts guy from the dealership and had him stop by to do it for me for beer in return)

Brought my Audi A4 2.0 B7 to the audi repair shop next door to my house (literally) after getting some stalling issues and a dreaded P0089 code along with a few others which were EASILY taken care of. I had the shop diagnose my car and leave the diagnosis open as I did the repairs and would return the following day to re diagnose it.

Started with the N80 EVAP Purge valve - cleared 3 codes and corrected the tank filling issue I had had.
Next was a fuel filter in hopes that I could avoid a LP fuel pump replacement -- replaced, cleared code, came back in the morning. Brought it back in and had him scan it again.
His notes say that the fuel supply couldn't keep up with the acceleration and suggested changing the in-tank fuel pump.

I had never done a job like that before. Between daily visits to the dealership parts center (front breaks, rear, coils, n80, fuel filter, coolant, rotars... All on separate occasions) I got the know the parts guy well enough to convince him to swap out the pump he was selling me.

The replacement was fast and easy and we didn't run into any confusion or issues.

Car started up fine after a bit of work, test drove it and the power was back, it didn't lose power on strong turns or have any of the symptoms I had before the replacement.

I then drove 30 miles to my girlfriends house without an issue. Turned off engine, started up fine afterward, let the engine idle for almost 10 minutes while waiting, took off and no problems still.

THIS IS WHERE THE PROBLEMS START. I pulled into a parking lot and had the car off for about 15 minute before I came back, started the car just fine and backed out, but right before I exited the parking lot the car stalls... ... That's when I notice my gas gauge is well over an 1/8 of a tank, however I didn't get gas after the install and started it with less than an 1/8th of a tank and 40 miles left. I figured the calibration could have been thrown off by the install so I called for a ride to the gas station and filled another 5 gallons and the car starts right up. Ok, scare is over, just figure out the gas gauge issue later. Well, now it's reading a half tank and I drive about 8 miles down the highway without an issue. As soon as I park the car I get out to scan for any codes because the light had come back on. While the car is idling it decides to stall again. Same issue. But this time I know I have gas. Try to start it a few times, no luck, get out of the car to figure out what to do, hop back in 10 mins later and the car start. This time I drive her home and leave her there until I know what to look at next.

Sorry for narrating my evening in such detail, just want to make sure it is understandable.

Is there a possibility that the pump could be installed wrong? What else could I check for?