New shocks are probably a good idea, perhaps some airbags too to help carry the load.
Oil and fuel filters should be pretty easy to DIY. Most places have a crazy markup for diesel oil changes. Fuel filters are easy to change as well.
Coolant, brake fluid, axle fluids, differential fluids should be changed too. Any idea about the maintenance history of the transmission? There are differing theories about transmission service... some people are afraid to change fluids on higher mileage transmissions. The "weak link" of that truck is the transmission. Stay on top of maintenance and consider beefing it up.
Truck shutting off, not a clue.