What was his boost at the time? Defueling occurs around 25
+ a couple psi. If that's the case, a boost regulator should help.
Another possiblity based on my past experiences: Does he have an in-cab fuel pressure gauge? I used to have a problem with no "top-end" power. I put in an
IN-CAB FUEL PRESSURE GAUGE (mechanical w/ pressure isolater). When I turned the key on, the pressure would slowly build to about 40 psi and after several minutes build to about 50 psi. When towing down the road at cruise the fuel pressure was about 40 and would drop to close to 20 when I floored it. None of this jived with what I had heard how a healthy fuel pump should performe. All of this was with the FPR already shimmed.
I replaced the fuel pump and the pressure immediately shot to 100psi on the gauge. I took the FPR apart, replaced the innards, removed the FPR shims and the pressure was then about 55. Now it would only drop off a bit, but no less than 50psi on the highway. I shimmed the FPR again to 65 at idle and it stays above 60 at full throttle. The "top-end" power was noticeably better.
