I still think you should put the regulator after the rails.

 

I prefer the FPR after the rails. I'm using a -10 main feed Y-d to the rails with -8, and a -8 return with a Magnafuel 750(boost-activated).
I had a similar issue when I made some changes to my fuel system and my surge tank was not getting enough air.

Could definitely be a tune issue though.

 

I have gotten to the point where I think it is weak coils because I know the valves are sealing, I know lifter preload is good, valvespring pressure is good, plug gap is plenty tight, plus the truck pulled all the way to redline, in every gear, every time, when the cam was a tooth off (would cause much lower cylinder pressure), and, after the cam was dot to dot (cylinder pressure back to normal) and turbo was changed, the only way the tuner could get the truck to make a full pull was to lean it out way too much (the richer the mixture, the harder they are to light, or so I'm told). Makes sense to me anyway. Please tell me if what I'm thinking is wrong.

 

I'll definitely plumb the FPR after the rails, if nothing else just to rule it out.

 

Where exactly is the FPR? I initially had mine just after the tank, and ran into a similar problem. I now have it setup properly after the rails. Plus if you are checking fuel pressure off of the regulator, you never get a true reading of what it actually is at the rail.

 

Mine is on the left hand side of the truck, just forward of the power distribution center.

 

This is what I was thinking. Where do you have your pillar mounted fuel pressure gauge plumbed in the fuel system? If it is not plumbed to one of the rails then you really don't know what the engine is actually seeing pressure wise......

 

Sounds a hell of a lot like fuel pressure dropping to me. Like they said I would stick the sensor on a rail if possible. I have seen issues on other cars where there was a restriction between the feed line and the rail causing it to show good fuel pressure before the rail, but not on the rail.