I have a Garmin nuvi 1450LM. I contacted Argent Data and purchased a GTRANS2. Note the "2". Scott does not list this device on his web store, but he was selling them a few years ago. The GTRANS2 is designed to power the Garmin nuvi through the miniUSB port where the normal GTRANS is designed to work with earlier nuvis that are powered through the unit's base.
Frankly, I was a bit disappointed by the GTRANS2 and nuvi 1450LM combination. It worked fine to provide NMEA lat/lon strings to the radio. And, the radio did send waypoints back to the nuvi to represent received APRS position reports. But, you had to refresh the screen to see those waypoints.
I do not know if Argent Data will still sell you a GTRANS2. I do not know if the GTRANS2 will work with newer nuvis. The basic GTRANS concept was designed to work with ealier nuvis such as the nuvi 350, but that model is long out of production and you can only find them on the used market.
At one time, I also owned an AvMap G6 APRS. As far as APRS position report mapping, that device works perfectly with the TM-D710. However, I sold the G6 because AvMap wanted over $100 for each annual map update which I thought was outrageously high. Also, the AvMap's user interface was too quirky for me to live with. Despite its faults, the AvMap G6 APRS is the only mapping GPS receiver/sat-nav unit that is specifically designed to work with the TM-D710.
Now that you can buy small Windows-based tablets and since the current TM-D710G includes a built-in GPS receiver, I would look at a tablet running APRSISCE/32 or YAAC to handle the APRS position report mapping duties. Microcenter's Winbook line of tablets will do the job. Steven Smith WA8LMF has a nice write-up about the Winbooks on his
web site. Also, you can buy refurbished Microsoft Surface Pro 2 tablets that will also do a great job for less than the price of an AvMap G6.