Question about fuel pressure

[Darkitec]

I'm trying to diagnose a problem with my 03 Tahoe, 5.3 flex, 93,000 miles. Instantly Developed a code P0300 issue last week, no power barely able to maintain 45 mph on the freeway.
Shut off the engine and it runs perfect, until I rev to about 2k, to 2500 rpm then the code and flashing check engine light returns.

Nearest GM dealer over 30 miles away so wont be taking it to them to fix.

I checked the Fuel pressure yesterday and it was low.

I'm concerned, after watching several dozen videos on Youtube, every one that checked their pressure the needle of the gauge was relatively steady, easy to see the pressure.

While checking mine, the needle was constantly bouncing (almost a blur) between 40 and 45psi.

My question is, is the needle supposed to be steady? or does anyone else have the bouncing needle?

And if this isn't normal, am I looking at a bad regulator, or fuel pump?

I'm not currently working so keeping the repair costs low is a big concern.

 

[georgebuhr]

I would recommend plugging it into a scan tool and seeing which cylinder is misfiring. pinpoint the cylinder, it may be more than one. I just bought one with 160,000 miles on it, and it spit back the same code, but no other info. So I looked on tool and saw three different cylinders misfiring, it ended up being three bad injectors.

 

[04gibbstahoe]

Fuel pressure should be around 48 psi at idle for a flex fuel. I think a little bouncing around is actually normal. Probably fuel filter or regulator. Pull the vacuum line off of the regulator and if fuel comes out then you need a new one. If not, change the filter. Good luck.