Welcome Mike, Good Looking truck! Why not fill out your signature line so when you post or ask a question people can see what you have? It will help us to help you.
How many miles on it? Any mods, besides lifted, leveled and wheels?
If you do not know the service history of the vehicle it is a Very good idea to change EVERY fluid in the entire vehicle so you can begin your maintenance schedule from a known value with good fluids..
Oil & Filter
Transmission Fluid and spin on filter
Power Steering/Power Boost fluid
There are threads on here to teach you how to do each and every one. Like anything else, you will save much money by doing it yourself.
A well maintained Duramax/Allison combo should go easily 500,000 if you don't abuse it. It is a Pulling Machine. The more you drive it, the more you will appreciate the wisdom of your decision to join the club
awesome! thank you for the helpful response. It has just over 100k I am actually getting ready to do at least the oil and filters this weekend. I would like to get all of the 100k mile services done because im not sure if they have been. I bought the truck about 2 months ago. Theres not a lot done to it other than just what you see. I'm wanting to possibly do a dpf delete to possibly get some better fuel mileage.