As a Fastrack user myself, If I may suggest, seperate one joint in your loop. Then with a DVM check the continuity at each joint in the track. I do this when I assemble any of my Fastrack. If I have a loose connection, I squeeze the rail slightly to get a tighter connection with the pins. Also, I would abandon the 3 walwart power packs and go with a 180 watt brick and the TMCC Lock-on. That will provide you with plenty of power and short circuit protection for your layout.
The links below are just samples. You can purchase from whomever.
Lionel 180 Watt PowerHouse Power Supply # 6-22983/85226 | eBay
Amazon.com: TMCC Direct Lock On : Arts, Crafts & Sewing