I compared the gauges on upper and lower helm stations today. The lower station tach said 800-900 rpm at idle while the upper station tach said 500-600 rpm (needles bouncing). Lower temp gauge said approx 170°( below the 180° mark) while upper said approx 140°(on the only line between 100° and 180° marks).
Any thoughts as to why the the lower gauges give higher readings than the upper gauges
I do not know in your case--but if the senders have been replaced I could see a problem. If the gauges or some have been replaced /mismatched it could--but not always present a problem. I have a 36TF which is similar to your boat -originally my boat had a upper and lower helm transfer ''switch'' that shifted everything from upper to lower etc and single station senders were used. If that system has been bypassed for some reason dual station senders are required. The fact that the upper gauges are reading lower values than lower ones point to some systemic issue as above. I would also and perhaps firstly look at that transfer switch as perhaps if the contact(s) is a bit corroded it would cause higher resistance and and a difference in readings.