I sold a 94 explorer with 180,000 miles on it. the guy is still driving it. When i sold it it needed a new seal on the gas tank and the 4x4 needed fixin but other than that i put 180k on it doing limited maintenance. oil changes every 3500, tranny pan got dropped once a year, differential fluids every 2 years and power steering fluid every 2 years. Only thing i ever had to replace was belts, spark plugs and a power steering pump.
the sport trac and the explorer are very close in design, i cant imagine much differences drive train wise. but as with anything mechanical...preventative maintenance is key.