85 K10 305 to 350

[donut]

What are your ultimate goals?
IMO, for all I know, what you have now may be what you really want. Just freshen them up and go. (and you know they'll fit without major problems.)
DD doesn't mean you NEED OD, sometimes OD and a high rear gear will hurt mileage.

Do you know your current axle ratios? RPM at cruise? And important, budget.
In my mind, easiest and most cost efficient way to upgrade the driveline is sell the truck and get a 3/4 or 1 ton. Ultimately, your goals and budget dictate.