I have not check fuel pressure however it seems to do it at all different rpms and throttle positions. Although at higher rpms it doesn’t seems to do it as much. I use the word surge but it’s hard to describe. When your under load, and when I say load I don’t mean loaded I just mean when the engine is under a load. You can hear the turbo spool and then not for a second and then spool and die again. When it does this the rpms fluctuate about 150-200 per the gauge although sometimes it feels like more. Almost as if you let off the petal some and get back in it. I guess the turbo vanes could be acting up but I hate to spend that kind of money and cross my fingers.