Appreciate the insight. What we found out after calling GMC PartsTech hotline is that the 1500' are built with a tray included solely because the engine compartment is relativity the same BOM as a 2500,which allows the option to add a second battery, hence the tray being there.
Secondly, the tray that was installed in my engine compartment did not have the proper hold-down lip or the adhered nut on the bottom to hold the retainer & bolt. This is the strange part as others here with 1500's have the tray that does have the ability to secure a battery. We brought in tray #22989633 and that also did not have the lip to hold the battery. My parts guy ordered tray#25826079 which is tray in the 2500 and that tray has the lip and the nut on the bottom which holds down the battery. The only difference is the slight jog for the washer bottle neck, however the tray will fit.
Lastly, the tray size requires an AC Delco battery Series 48PG (or similar battery) not a Series 94 which is included with the 1500' truck and 3 inches wider. When you order a 2500 with dual batteries, you receive 2-48 series batteries which includes an isolator.
I ordered the GM factory cables for a dual battery install and will have my installation shop add the appropriate isolator and fuses.