I am not sure on the boost level on the 1st gen trucks. 15 may be close. I doubt it is over 20. Generally if you do not have enough fuel you can not make boost. I have heard of weak lift pumps causing a lack of power. Not sure what the fuel pressure should be for that style lift pump but as long as it has positive pressure to supply the injection pump it should be enough to give the pump all it needs. Dirty of partially plugged injectors could also play in. Mine can hit 36 on a good day. Lack of fuel is the usual culprit. Fuel lines sucking air, weak lift pump and clogged fuel filter are the most likely. When was the last time you changed the fuel filter? Apparently it's still in the future, unless you live in a time warp or something.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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