if it was used as a work truck that was "abused" as far as maintenance goes, i would go and change all the fluids and filters it has. much better performance, reliability, and it will make it last longer. ideally, you should do ALL of these as soon as possible.
flush cooling system, new coolant with SCA, same color as original.
new engine oil and filter (you already have)
fuel filter
flush transmission fluid out (replace with synthetic optimally,) and a new filter
flush power steering system out with ATF
change transfercase oil (if 4wd)
change front and rear differential fluid