W/ that many miles…I say you could go either way depending how you use the truck & how long you intend to keep it. If it’s your DD & you use it like a truck to do truck stuff a lot & you put a decent amount of miles on it (10k+) I’d say do the suspension first & if you’re gonna do the leafs you may as well do the shocks - if they don’t need to be rebuilt @ 50k they WILL need to be rebuilt by 60-70k even w/ normal use.
Then the tune b/c you’ll be able to get into the throttle more w/ the suspension freshened up esp the rear leafs
If it’s just a 2nd vehicle you mess w/ & don’t put that many miles on save some $$$ & just do the tune for now & worry bout suspension later esp if you’re not 100% certain you’re keeping it- you can always return to stock & sell the tuner or recoup some cost & reuse on another vehicle etc
If you blow $3.5-$5k on suspension work & then get tired of it or trade it in within 2 years…kinda a. Waste
Lastly…I was on the fence & had trouble deciding what to go w/ for the rear - i decided on +3HD & am very glad I did, already appreciating the extra payload & no sag w/ heavy cargo & it’s definitely not too stiff- & I have the front springs compressed about 1.25” too- not too stiff at all IMHO