Hard start, shuts off when transmission is shifted into gear, where is the fuel tank pressure sensor located?

Hello, it looks like the Fuel tank pressure sensor is inside the tank, but you can check the wiring at the connector to see if it's actual high pressure or if it's a bad sensor. Even opening the gas cap or unplugging the Purge valve hose should cause the pressure to drop. If the 5-volt reference is shorted to the signal wire somewhere, that will also cause it to read high pressure. Just unplugging the connector on top of the tank if you can reach it should cause the reading on your scan tool to change, just so you don't drop the tank if it's a wiring issue. I'll post the diagrams for you.

Actually, it doesn't look like it's in the tank, just on top of the sending unit, not sure why they have it listed inside the tank like that.
There should be 2 connectors on top of the sending unit, are you seeing something different on your vehicle? The service info is very different than what you're describing.
The Tank pressure sensor has to be on top of the tank somewhere,
Are you reading a Purge data pid on your scan tool?
It looks like the same location on every size Savana, the 1/2 ton, 3/4, and 1 ton.
How many wires do you have at the connector on top of the sending unit?

The 02 Savana 1 Ton Van is the closest vehicle we have information about. The Tank pressure sensor has to either be on the fuel vapor hose, so an inline type of sensor, or possibly on the Charcoal Canister. It has to be somewhere where there's going to be vapor pressure coming from the fuel tank. I have heard of them being inline on the vapor hose, but I just don't have additional information for an RV. But I'll keep looking. Post your vin number and Ill try looking up the vehicle by that.
Is it a Cutaway, not cutout?
This is what an inline vapor pressure sensor would look like, so if you follow the purge valve hose back towards the rear of the vehicle, you should find it.
This 2nd picture is from a Honda, but this is an example of a Fuel tank pressure sensor that's part of a combination setup, so you may have to look more around the Canister area. It's going to be a 3-wire sensor. Obviously it's not in the regular gm location. But just to show that they can be in different locations. Really trying to follow any vapor hose is going to be the trick to finding it.

Okay, it is coming up as Express 1 Ton Van on that VIN. And still shows the FT pressure sensor in the same location, Part of the Fuel pump module. Are you getting any codes for the Tank pressure? I see the lost comms with ECM, but are you only seeing the pressure sensor pid reading maxed out and no codes?
It's just super strange that you're not getting any evap codes or purge, vent valve, etc. Nothing like that.
Let's go with the starting issue, what happens to your fuel rail pressure when it goes to stall? The stalling out should be setting some kind of code, have you taken a look at live data through the Global OBD2 side of the scan tool and not the manufacturers side. Global obd2 might come up with either some codes or data that differs from the manufacturer side, I mean the stalling out when under a load suggests a fueling issue, I would start on some diagnostics with the stalling issue first and see if fuel pressure is dropping off. Or possible oxygen sensors that are stuck at a certain voltage, those types of things. Your scan tool might be giving you incorrect data pids, I use Autel too and there's always a million updates but have always been told to take a look at global obd2 and mode 6 data.
This has one of those fuel metering body assemblies like the diagram below. These are known failure points if it has one of these. They are known for the injectors sticking closed, there are multiple TSBs on these fuel systems.
I wanted to show you the FTP sensor voltage readings. High pressure would be low voltage, so if you're reading high voltage, then the pressure in the tank would be low or in a vacuum.

Well doing the injector balance test is how gm service info says to check those, they used to have the old-style injector tester. The fuel pressure spec is 60 to 66 PSI, so if it's staying there at 62 that's okay, but it shouldn't be going back into open loop. In open loop it only calculating its fuel strategy from the coolant temperature sensor, map, MAF etc, and ignores the 02 sensors until their voltages are swinging enough, so the ECM might not be seeing a good signal form them, or it might need a hard reset. Below is the description on Run modes. If the RPM is too high, it might go back to open loop. But it sounds like you may want to reset the ECM and check the 02 sensors in Global obd2 data and see if there's a difference. Having to keep your foot on the gas to keep it running tells me there is not enough air flow, or the pulse width on the injectors is too low. Have you pulled any plugs to see what they look like? Go back to the basics on this one. You might have the correct fuel pressure but not enough volume, dirty MAF, EGR stuck slightly open, those are things I would check. Since its a 5.7l the MAF should be around 5.8g/s at idle, I would graph all 3 oxygen sensors and see if the front 2 are swing and the rear one is steady. If all 3 mirror each other that points to a bad Cat.
These are all the things I look for in live data, and Im not sure what Autel you have, but they do pretty good with the amount of live data PIDS they provide. There's something there that will be out of place,
But the open loop is the clue, its reverting back to it because it's not seeing a good signal from an oxygen sensor, or the sensor is too slow. When they get lazy and frequency is low, it will go back to open loop as well. It does sound like the Fuel tank pressure is high, so it's possible the vent valve is stuck closed or something, but that wouldn't put it back into open loop. It would just fail the Evap readiness monitors and set a code.
Can you get a pulse width on the injectors for this vehicle, I know you said your fuel trims are good, but with no codes, that data might not be correct. But go back over data again, If the vehicle has secondary air injection, that's something that will cause a false 02 reading as well.
Sorry for long post, I added some more run mode info below that might help.