Low fuel pressure after making pass down track

I was checking over some things on my Duster before taking it to the track for the first time and noticed the fuel pressure gauge bouncing all around.
I tried to adjust it either way with no effect to the fuel pressure gauge whatsoever so I replaced it. After replacing it was reading steady 8-9 with no bouncing so I tried to adjust it to 6.5 with no change so I replaced the regulator.
After having a new fuel pressure gauge and a new holley fuel pressure regulator I was able to set the fuel pressure at 6.5 psi and thought all was well so I hauled it to the track. After backing the car of the trailer I noticed fuel pressure was back down to 5psi so I put it back at 6.5.
Before making my first pass I drove it around the pits and checked it one more time and it was fine still right at 6.5. After making my first pass I got back to the pits and with car still running I checked my fuel pressure and it was down to 3 psi.
I'm using the stock (brand new) tank going into 3/8 rubber Line with one plastic filter inline into a mallory 110 gph pump. Running out of the fuel pump is 1/2 aluminum fuel line eventually spliced into steel braided 1/2 line to make the sweep into the engine bay. Car is a 71 Duster 460hp 360. Car has no return line currently.
Also not sure if this is related I'm not too confident in my regulator location since everyone else has theirs in front of the toward the front of the car ahead of the carbureter. It's just a 12 second car but could Gforces not be allowing fuel into the carb fast enough because it's working against gravity while the car is launching? Here's a pic with my regulator/gauge set up

Thanks for reading

If the gauge doesn’t have an equalization valve on it, with it being above the engine the heat will cause the pressure in the gauge housing to increase. This will increase the pressure on the outside of the bourdon tube that actually causes the needle to move. This will cause the gauge to read low. I use an aeromotive gauge that is liquid filled with an equalization valve. I’m also going to make another suggestion. Having the gauge over the engine with all the vibration isn’t a good idea. I’ve had one fail mounted that way and spray gasoline all over. That with a hot engine could be a mixture for disaster. If the regulator is mounted on the inner fender or some where off engine put the gauge on the output side. Better yet set the regulator and remove the gauge. Here’s a good read.

Fuel Pressure Gauges - Aeromotive, Inc

Electric pumps do a better job of pushing fuel, than pulling fuel (just FYI). Make sure your pump is in position to be gravity fed, also (since your tank is new) I would put my fuel filter after the pump if you are comfortable with that (mine is setup like that for my race/street car). Some folks do a course filter pre-pump (like 100µm) and a fine filter after the pump (about 40µm)...just food for thought. Also, if your sending unit has that little sock on the end of it, I would remove it. Those can cause headaches....

On the carb side, when this lower pressure event happens, is the car running? If so, do you hear anything weird like the carb loading up? The reason I ask is, you could be pushing fuel past the needle & seat and drowning the engine in fuel (with the air filter off it would look like a fountain coming out of the vent tubes).

One last thing I would check is your pump. Does it sound different when the pressure is low?

I'm not sure this is the answer in your particular case, you may be dealing with a heat or othere issue
However it may be helpful in understanding how pressure regulation relates to flow into the bowls.
Often running lower pressure will result in steadier pressure during the actual run and better provide a better rate of flow.

Here's some info on the Mallory Pump
Holley/Demon Carb stumble

The experiment more or less starts here
Holley/Demon Carb stumble

read down for his test results

Tape a gauge to the windshield so you can figure out what is actually going on before spending a lot of money. IMO a return system is a must with today's pump gas.
Fuel Pump and Vacuum Tester

Don’t like cheaper liquid filled gauges. The heat makes them fluctuate like mad. Watched my car idle with one having zero fuel pressure for 30 mins. Drained the gauge and its rock steady. I run a big mechanical and a holly red at the tank. Rock steady pressure. Plus the Holley helps it start after the fuel evaporates out of the bowls.

Is your tank properly vented ?