As a veteran TRX-1 user, my advice is as follows:
1 - Don't try to trunk track immediately--instead, search for or scan known STARS control channels in conventional mode and see what the radio actually picks up.
2 - Once you've identified what control channels you're actually receiving, check the listing to see just how many Div.4 and Div.6 sites use that frequency. Div.4 covers a lot of ground, and some western sites might not carry Div.6 traffic.
3 - Know that you can 'lock out' a given site--but that you will still receive that site if the choices in the radio include another site with the same CC freqs as the 'locked-out' site. Whistler doesn't recognize Site ID's and I suspect that Uniden doesn't, either. You could be receiving Poor Mountain and your radio could think its a site in Fairfax or Virginia Beach.
3A - The problem in #3 is exacerbated if you load ALL the channels in a given site. A voice channel at one site might be a CC at another site and vise versa. You might try downloading control channels only.
4 - You may not solve everything at one time. If you find a good site, but it switches control channels, you may encounter a new set of the circumstances described in #2 & 3.
5 - Depending on your desires, and what else you're listening to, a directional antenna might help. It just depends on what level of priority you have on picking up Div.6, and what sites you can receive from your location.
Let us know how it turns out.
73/Allen (N4JRI)