New to me 09 prostar

[earnies2]

Hello and great forum

I just purchased a 09 Prostar premium it was a Werner truck 435st cummins CPL 2732 13 speed trany Verry clean runs good I bought it from the 2nd owner who bought it for his brother in law to run the road and he leased it on with Landstar his brother only ran 30k in 6 months and gave him back the keys the truck sat for over 8 months while trying to sell for 55k he bought the truck from Jorden Truck Sales and Jorden put a new EGR valve and a EGR cooler on it the the new owner put 8 new Yokohamas on the rears new a/c compressor,receiver drier and expansion valve..truck has a Thermo king APU that works power invert-er,and diesel heater under the bunk that also works.....

1, The a/c in the bunk is ice cold the dash is only cool I did find the unit that opens and closes the blend door to be erratic and ordered a new one but don't think that is the problem even if i manually close the blend door it still isn't great i happen to notice there isn't any shutoffs for the heater core thinking they were removed when the APU was installed? only a thought

2, there is 555k on the truck should i do the rods and mains or do an oil sample and see what it says ?

3, should i run the overhead?

4, should i clean the DPF and the intake also change the doser valve..what is the cost to do this? I drove the truck from upper state NY to Boston with no lights or problems I am just looking to possibly avoid any problems on the road....Thanks in advance