Hi,

Just a thought regarding the low fuel warnings. Depending on how you are calculating your fuel load, ie Simbrief etc, the reserves figure you enter into the FMC is important. So if you enter say 2.0 as your reserve fuel load (with a total load of say 10.5) when in fact you figure should be 3.0, you will get a low fuel warning when the FMC calculates your landing fuel will be say 2.5.
I have only had the 757 since Christmas so still getting used to it. I have noticed fuel consumption can be heavier than predicted by Simbrief. As for your performance, very odd. Like you I bought a new system I7-8700 GTX 1081i when I moved to P3DV4 from FSX. I have found the 757 performs better with higher settings than the FS Labs for example. That said, with ASN in bad weather, that can reduce performance on all my aircraft.  Not sure if this helps.

Best,

Keith