Inspector should work in windowed mode—it's Control Panel that never does—but some players do need to cap the fps slightly higher or lower than 60 to see results. Of course, if you're in windowed mode and Inspector isn't doing a thing for your frame rates, it's time to try something else. MSI Afterburner and RivaTuner Statistics Server are both good options; I use RTSS for my AMD card, and it works very well.
Screen tearing is somewhat common with TS3, but you should be able to get rid of it with the right tool. It does sometimes take a bit of experimentation to find the right settings. Fussing with these tools is not really my area of expertise; you might want to ask for advice from igazor, or SimplyJen, who put together the screenshots I linked above.
I'm also not sure why your game would crash transitioning from fullscreen to windowed mode, but if that's the only issue, you could just stay in Windowed Borderless Gaming. Are you playing in a custom world again, or do you still get crashes in a world like Sunset Valley or Riverview? And how much RAM is your game using? You can check in the Task Manager; if it's showing percentages of memory, you can right-click on the Memory header to see the absolute amount. Over 3.5 GB RAM, the game is in constant danger of crashing.