Rajah Caruth’s return to Spire Motorsports in the Truck Series should have been a happy reunion. Instead, it was bittersweet. Caruth stepped in for Kyle Busch following his tragic and untimely death earlier this month, driving the No. 7 Chevrolet in Nashville for the Truck Series race this weekend. It was a great opportunity for Caruth to make a mark with his former team, but a difficult moment nonetheless, as he admitted. “Obviously, it’s been …