test port on a th-350
Not positive about this fact for a th350, but on a 700/4L60E the test port will pretty much tell you the actual transmisssion temp... Just make sure the sender your using does not block the passage that the port taps into 
Ive always put the sender on the outlet side of the cooler though, to let me know that my coolers working properly, and it gives you an idea of what the vital transmission parts that get fluid first are seeing for temps.
The port tells you pretty much what the pan fluid temp is, as its (usually) located just before one of the last components before the fluid goes back to the pan to be filtered and pumped out to the cooler.
Ive always put the sender on the outlet side of the cooler though, to let me know that my coolers working properly, and it gives you an idea of what the vital transmission parts that get fluid first are seeing for temps.
The port tells you pretty much what the pan fluid temp is, as its (usually) located just before one of the last components before the fluid goes back to the pan to be filtered and pumped out to the cooler.
