A lot of things in this truck does not code, even for a 99.
For it to code, there should be a sensor of some sort.
There is no sensor in the Lift Pump or PMD.
A lot of codes are to warn about Injector Pump conditions or boost condition.
1995 GMC Suburban:
PMD in Bumper
Leroy Diesel Flight System PMD
Leroy Diesel Oil Cooler Line
4" Warpspeed Exhaust
Kennedy Diesel LP/OPS Harness
Bosch Duraterm GP