def. google the airbrake tests on youtube,watch and take notes and print out the ones on line(cdl pre-test's)
as for the 5.9 it's a good engine, more important is which trans it has
you can crawl under the bus and look at pad life left as well as brake drum grooves (take a flash light with you) ask a heavy vehicle mechanic what to look for (class 7/8 trucks) most truck repair places will answer basic questions and such