My engine is stock with the exception of the cam and external bolt on stuff, mine holds 25 - 30 at idle and close to 60 at cruise, with about 80,000 on the clock. I run 10 - 40.
Those are good numbers , but 10 at idle 25 at cruise could be within spec but borderline at best . I'd hook up a known good mechanical gauge and check and make sure , thicker oil is not a soloution