If it ain't broke....
There really is no such thing as a tune up on a diesel- there are no plugs to change, no distributor cap or rotor, the only timing is the injection pump, and if it is working it is working. it either runs well with no smoke, no hesitation and no bogging or it doesn't, fiddling with a decent running engine won't do much. Make sure your fuel is clean, your fuel filter is clean, your coolant lines are clear, you raw water pump is good, the air intake is unobstructed, check the intake and exhaust valve adjustment, and run her. All of that you can do yourself in a coupe of hours with a manual. if you don't have a manual, and need the specs on valve clearance, let me know and I will scan the relevant pages from my manual.