How hot does it get where you live? How hard do you use the PS, and do you have Hydroboost?One a related note, this truck has the frame mounted loop cooler style of power steering return line. I see that it's discontinued and no longer available anywhere. Pretty sure mine is still good, but if not will it do any harm to remove that cooler and replace it with a standard return line?
The in-frame "cooler" was leaking when I bought my '97 K2500. The thing carries around a V-plow for snow, so the front end is heavily loaded, and it has Hydroboost. OTOH, the truck rarely leaves my property. I ran bulk PS/Trans Cooler hose to bypass the in-frame cooler; cost me a couple of clamps and maybe eighteen inches of bulk hose.
Figured at the time that "someday" I'd put a real, front-mounted cooler on the truck. So far, it hasn't made it to the top of the priority list, and it's been several years.
Any commercially-available PS fluid suitable for GM will be fine. I do not expect that "synthetic" fluid is going to be a significant improvement.
The boxes the pumps come in may have different names on them, but I bet they're all "rebuilt" by the same company and then custom-packaged. The "new" pumps are likely direct from Communist China.
If this were me--and it isn't (so far) I'd find a low-mileage unit at the Treasure Yard.
Consider installing a PS filter into the return hose.