chuckbucher: The auxiliary guage package is a known error-prone accessory.
By that, I mean that a couple of GM people have told me that it is VERY easy to short the assembly during the installation process. This has the effect of permanently killing the assembly (whole 3-instrument cluster has to be replaced).
Usually, all 3 guages are kiled as a result of the error.
In your case, if just the transmission temp guage is intermittently not reading, it's more likely a bad (intermittent) connection on THAT individual guage's signal.
Have your dealer check it out, but be sure to tell him, if he does not already know, about the shorting problem. I lost my 1st cluster to that problem.
Also, I didn't notice if you have an 03, 04, or 05 SSR.
The 03 and 04 use one cluster (Volts, gallons per hour, and transmission temperature), while the 05 uses an entirely different one (Volts, torque, outside air temperature). They are obviously NOT interchangeable. If the wrong one was installed, the readings could get interesting and "intermittent". The cure here is to get the correct cluster for your year of SSR.