The x17z would be better weight wise but I would go with the tandem axle tt even if it's heavier. The T4R can handle the weight, the only concern is the tongue weight without a WDH. Consider having a custom made receiver made. The tandem will provide better stability, be safer in the event of a blowout, smoother tow etc. Depending on configuration the tandem will usually end up with a lower tongue weight once loaded as well.
I wouldn't be too concerned about the trans temp if you have a trans cooler. The T4R computer reads it, even though it doesn't display it, and will set off a dash light well before any damage would occur. The scanguage won't help. It plugs into the OBD port and will display many readouts, but trans temp isn't one of them. Can't remember why but if you search the topic on T4R.org you'll find lots about it. Some said they were able to modify it to work but it never did for me.