In making his Trans Am debut as part of a cameo appearance for The Racing Academy squad, the Supercars driver finished third after starting seventh in the 21-lap encounter at Symmons Plains Raceway, which was won by James Moffat.
However, the result would not last, with Slade slapped with a five-second post-race penalty for contact with Owen Kelly, elevating the latter to the podium, with the former ultimately classified 13th.
Slade was not the only driver to be issued with a penalty, with John Holinger handed several after contact with Jett Johnson on the opening lap of the race.
Johnson went on to finish 16th on the road, one spot behind Holinger before the penalties for the #23 Holinger Racing Camaro were applied, switching the two for a last-place result for Holinger.
The National Trans Am Series will return to the track for Race 2 at 12:20 local time/AEDT, with Race 3 to take place at 15:25 local time/AEDT.
The final day of action at AWC Race Tasmania will also see races for the Supercheap Auto TCR Australian Series, S5000 Australian Drivers' Championship, Gulf Western Oil Touring Car Masters, Tassie Tin Tops and Hyundai Excel.
Saturday saw Ryan Hansford and Steven Johnson pick up a win apiece in the Touring Car Masters, while Bailey Sweeny claimed the opening TCR Australia Series race, after polesitter Will Brown missed the opening encounter due to a mechanical issue.
The 2019 TCR Australia Series title winner will return to the track today, after his Audi RS 3 TCR was repaired overnight.
All the action can be seen live and ad-free on Stan Sport for Australian viewers, with live and free global streaming outside Australia via Speedcafe.com here.