Hey everyone- I have just taken possession of an '07 5.9 3500 Quad cab with the 48RE. Thing has 100K Miles, owned by my family since new. Never worked, lifted, tuned etc. Stock size michelins. I just did an oil change with a Fleetguard filter and Delo 400 15/40 Blackstone sample says no issues. New redhead steering box and flushed out steering fluid with ATF+4. Flushed brake fluid out and replaced front rotors and calipers. Air filter. I plan to change the diffs with synth. 75W90 and Xfer with ATF+4 and lube all drive line zerks.. Any comments? Im interested in what to look out for on the motor for longevity, I have no interest in suspension lifts or more power, just reliability. Thanks for any help. I have a Diesel Land Cruiser which I've blown my brains out modifying for off road adventures and dont want (cant afford) to go down that path again!

 

It's addictive, innit it. Ooo, something ELSE I can modify!!!

If you use the truck for heavy hauling/towing, the older trucks recommended I think it was 75/140, which is indeed synthetic. Don't know about the newer ones, should be something in the owners manual, which you quite likely actually have.

Service the trans?? Fluid/filter change is you should really need to do.