FRB-5 pumps almost exactly double the amount of fuel than a stock lift pump does. I measured almost 2liters/minute from the fuel manager drain (with engine off) with the FRB-5 and only 1 liter/minute with the stock 96 pump.
Even on my hottest tune, WOT for extended periods I cannot drop the FRB-5 below 3psi, and that is measured after two filters (pre and post) before fuel enters the IP.
My pump may be shot or I may have excessive return from the IP. Few blips of the throttle in park and I can drop the higher pressure Walbro to 0 and continue to a vacuum depending on the prefilter in use. Also the Walbro screen is too fine for biodiesel. I need the course screen. (In fact I need a better 30 micron prefilter.)
Good to know as I was thinking about 140 GPH pumps to help...
When I changed turbos I could not get enough fuel out of the Heath HO LP to feed the IP either. I changed to the FRC-10 and have been very pleased. Granted I still need to do the FTB mod. Perhaps a bypass like Bruce has done and get rid of the FFM altogether!
I know the ATT can kick the GM-Xs butt. Fine tune your system and you will be a happy camper... Pun intended.