So it sounds like this piano player is really bullying you about your playing up there. Could this be causing tension? (Physical)? Have you noticed this problem before playing with this group? Do you feel yourself thinking about it before you go up in that range and then worrying after you've played?
I am with all of the above about not using the tuner. When I work on my intonation, I use the tuner function on my Dr. Beat, and listen for resultant tones at various intervals (both on my BERP and on the horn). It's kind of cool...Try Schlossberg #4 as a series of 4-3 suspensions or Major to minor 3rds or P5 to tritones!