Phoenix in the No. 15 and a full race at Homestead in the No. 01 (ironically his old number in the Cup Series from 2003 to 2006), where he would finished 10th in Stage 1. In 2018, Nemechek took over as a driver at NEMCO Motorsports after his son John Hunter moved up to the Xfinity Series with Chip Ganassi Racing. He had also been announced as one of the drivers of JD Motorsports' No. 15 car, splitting the ride with other drivers. It was announced that Matt Mills would drive the 15 full time. Nemechek ran the PowerShares QQQ 300 in the 15, and later returned to the car for the Fitzgerald Glider Kits 300. 2019–present Nemechek would once again run primarily in the Truck Series for 2019, splitting time between the No. 8 and 87, sharing the trucks with multiple drivers. Nemechek also returned to Xfinity competition, driving the No. 13 for MBM Motorsports, and the No. 17 for Mike Harmon Racing. In September, Nemechek raced in the Monster Energy Cup Series for the first time since 2015, returning to Premium Motorsports (formerly Identity Ventures) in their No. 27 car for the Bojangles' Southern 500 as part of the annual throwback weekend. Nemechek later drove at Las Vegas Motor Speedway for the team in September and said that more races in 2019 or 2020 weren't out of the question. Nemechek and his son John Hunter made motorsports history at ISM Raceway in early November 2019 by being the first father-son duo to race in all three main series in one weekend. On November 15, 2019, Nemechek surpassed Richard Petty as the driver with the most starts in NASCAR's three national series, at 1,186. In 2020, Nemechek returned to Mike Harmon Racing in the Xfinity Series, driving their renumbered No. 47 car for the season opener at Daytona as well as at Las Vegas and Phoenix. Nemechek was scheduled to drive a third part-time car for Mike Harmon in 2021, but NASCAR's lack of regular qualifying halted those plans. Nemechek attempted the Truck Series opener at Daytona, but lacked speed and missed the field for the second year in a row. In 2022, Nemechek returned to the Xfinity Series, driving the No. 24 for Sam Hunt Racing, partnering with his son John Hunter, at the Wawa 250. However, he failed to qualify for the race after rain cancelled qualifying.