mystery inc.

i have a dawes device afr gauge.had my car mapped a couple of months ago.but from day one the gauge seems to read good on fuel till it gets to 600 rpm.then it shows lean.the boost settingf that the car was mapped to has not changed.is it just thius type of afr gauge thats readingt wrong?i cant see it being the map thats the problem.what afr gauges do you lot use? or do you use any.?i have a apexi ecu plus cmmander and the knock does not go over 26% which is normal.at high speeds.