I believe the Thrunite TC20’s protection circuit in the battery is what prevents full turbo. There was a big discussion about it here. Try an unprotected cell or remove the circuit from the stock battery, then the output will jump up.
You can verify your readings by measuring how many amps you get at the tail cap. It should be about 9A iirc. Even at full power you will not get 3800 lumen. About 3200-3300 is the most you can expect.
I’m not familiar with the G35. Has anyone verified that it can do 2000 lumen?
You should also mention if your light is a cool white or a neutral white, because that can also affect the readings. Almost all manufacturers will give the lumen rating for the cool white version. Typically, the neutral white version will always read less.