I have one in my truck. It is supposed to have 2 ATF temp sensors but only one returns data--and yes, I entered in the code a second time, triple checked, and it simply won't work. But otherwise it works just fine.
I used to have it in my Jetta, and found it was a lousy tool to track mpg. I could "calibrate" it and it'd be fine for a few tanks, then I'd alter my driving habits, and it'd be significantly off. I'd drive conservatively, get 47mpg for several tanks in a row, and SGII would report that. Then I'd get a bug, drive hard, and get say 42mpg calculated--but SGII would report something like 39. Not close. Not a problem here, since I think your Mirage has an mpg readout and you weren't asking--but will point that out. In my truck it seems "ok" but I rarely drive that hard, so I don't know if the issue still exists or not. [It's like a sample rate error, I think. No idea, gave up caring, if I want more mpg then I know how to do that, don't need a gauge to know when I'm misbehaving!]
I want to say, couple years ago, on the Mirage forum that I read of issues with SGII on the OBD port. Like the car was having problems with having a reader that was plugged in all the time. Maybe it was unrelated, maybe it was FUD. Point is, I'd go there and look for it, if you can't find it maybe it's a non-issue. But of all the people who would know what code to enter for transmission temperature, they would be the ones.
My SGII did lose its backlight after a few years; I had to open it up and fix some cracked solderjoints. No issues otherwise in what must be 10+ years now.