Within tolerance means within .1 to .3 difference; like your true peak measurements are showing.
Anything more than that (a full LUFS) would mean something is not correct.
Are you sure you are running the latest version of Dolby media meter? (Which has both 1770-1 and 1770-2)
Also be aware that all “dialog” readings within the DMM are based upon dialog recognition (as in the LM100), which is not part of the R128 specifications.
All I can say is that from the tests I did, on both real life content and EBU test files, the SLM128 is perfectly within specs, and on par with any other meter out there.
Fredo