Hey Jim what alot alot of these guy's that support the 03-04 wont tell you is that the 03-04 os pretty lame when it comes to electronis HP mods, and some bolt ons.
A 04. 5+ will ALWAYS have more hp mod vs mod dollar for dollar over a 03-04
I asked the same questions you're asking right now and people feed me the same info. But I soon found out that alot of cool stuff was NOT avaiable for the 03-04. The Smarty puts down 40+ more HP in a 04. 5+, you can only get BDDL Crazy Larry in 04. 5+ (220+hp) you cant enable any cool factory features like idle-up and cold start. There's alot of people out there putting down awesome numbers with their 04. 5+ with simple bolt on's. I'm talking about 600-650 HP on a single charger, no injectors, no cp3 mods, no twins, no No2.
I know you said it's not about performance but I feel like someone needs to tell you this. It just goes to show how much better the technology is on the 04. 5+. I have a 03 HO and it doesnt get the greatest mpg. There's alot of newer trucks getting better mpg. Maybe if I didnt live in the mountains and lived where its flat and set the cruise to 65 everyday on the freeway id get better mpg but I dont.
Yes I love my 03 HO but I wish someone would of told me about the other differences between the two. You say it now that it doesnt matter but I can easily see you wanting to add a Smarty or something similar and then the vicious cycle begins.
Goodluck
BigDan (poor 03 syndrome)
Oh a side note the 03-04 and the 04. 5+ become equal at the really high levels like 650-700HP once you changed out all the parts.