Looking at a used 2003 4x4, Auto, 73K on the clock....

[cerberusiam]

Yep, you have an 04. 5. A smarty will tune a lot of the emissions stuff out, increase your power and mpg in the process plus all the extras it offers.

A gauge at the CP-3 is the only way to verify you don't have flow issues, but, a 3 um filter between the OE housing and the CP-3 should not tax the stock pump and will be a huge step in maintaining the high pressure system. Regardless of what you do a fuel pressure gauge is a good investment.

The only thing better would be an additional water seperator between tank and OE filter.

 

[HHhuntitall]

Stick with the 15-40 weight and a brand you like. Valvoline Premium Blue, Rotella, etc, are easily available and work well.

Upgrades for longevity get a lot more involved. If your engine plate says 325 you have an 04. 5 emisisons engine. Check build date to be sure, should Jan 04 or later.

Biggest mechanical changes between the 305 and 325 is the cam profile and better valves\seats. Electronically, additon of a 3rd event and a remapped timing\fuel map. The combination made it 50 state emissions compliant but cost some mileage. A Smarty will allow adjusting some of that.

Fuel pump is an issue when you add the needed filtration. Best thing you do for the engine is add an addtitional water sperator at the tank and a solids filter in front of the CP-3. Then the pump becomes the problem becuause it will not draw correctly thru another filter. Check to see if they upgraded to the in tank pump, you may have it.

..... and a piston design change. The bowl is not very deep on the later, 325hp trucks, and they are prone to blacken the oil a lot quicker than the earlier trucks, in my experience. SOS shows it's mostly combustion related, so I'm guessing it was a change prompted by emissions, and the oil takes the toll... .

Regardless, it's still a good truck to have, certainly better, IMO, than the later 6. 7L trucks. Fewer problem areas, I think. Certainly good advice from all above.....