I photographed this PSI MB-4 aircraft tug at Oshkosh during EAA AirVenture in 2024 and 2026.
Though they are named the same, this is quite different than the Coleman/Entwhistle MB-4 or the NMC-Wollard MB-4 aircraft tugs.
PSI MB-4 aircraft tug
Oshkosh 2024
Believed to be the same tug with new reflective strips added