Lower vacuum reading just of idle ????

Background Info:
- working on a 1997 Rolls Royce Silver Spur with a 6.7L V8 turbocharged engine
- fuel management system uses a MAP sensor to determine load (i.e. speed density engine)
- vehicle has been driven ONLY 100 miles in the last 2 years
- vehicle needs to pass smog
- no trouble codes present
- limited OBDII data PIDS - could only retrieve STFT for Bank 1 (there is only fuel control on one bank anyways, so we are good that way); at idle, STFT hangs around 10%
- work completed since Silver Spur has been at our shop - A) replaced tired and cracked vacuum lines replaced front O2 sensor C) replace rear O2 sensor D) sea foamed the engine by spraying cleaner in the intake E) smoked intake for leaks - good F) checked fuel pressure with a WOT run G) test drove the vehicle

Where the diagnostic procedure is now at:
- see the attached pic
- frames 60 - 70 --> STFT at 10%; Intake pressure at 33-34 kPa; throttle position - 0%;
- frames 71 - 104 --> STFT - steadily drops to about 5.5% (frames 100-104); intake pressure at 29kPa; throttle position 5%; engine speed 1350 rpm

What I don't understand:
- I have better intake vacuum slightly off idle - ???????????

What I THINK the problem is
- 10% STFT at idle is alot (i.e. double digits)
- double digits fuel trim numbers usually suggest fueling and/or mechanical issues
- I THINK I have an engine mechanical problem (i.e. compression rings and/or valve train issues) as the idling kPa of 33-34 (i.e. about 17.5 in Hg) is not as good as it should be; my experience of good vacuum at idle is about 22 kPa (about 20-21 in Hg)

What gives on this one????????????

As always - thoughts appreciated.