How to measure GPu temperature MBP 13 mid-2010?
I used to have an MBP 15" mid-2010 and I was able to measure a lot of temperatures (including, I'm fairly sure, the GPU temperature) using iStat Menus. They have a 14-day trial version so it costs nothing to try.

Edit: here's a crop from a screenshot on my older MBP 15" mid-2010 showing the latest version of iStat Menus. Notice the plethora of GPU sensors.