I bought a Chinese Gates pump, and the shaft seal pooped out in a year or two. It got replaced by an Airtex, that seems to be doing ok. I don't drive the truck very much anymore, Though. If I were to try another cheap waterpump it would be a GMB since they are a Japanese OEM. I have a genuine GM casting to send out for rebuild, at some point. Unfortunately, I don't have my original casting. I kept it for awhile, but got tired of having it under foot, and got rid of it.
Before spending big bucks on a new GM pump, I'd have to be sure it was US made, and not a Chinese import.
Make sure the block is clean. I've used various sizes of wire wheels to do that. I've coated the gaskets with a spray on sealer, but I think only to the pump side. I don't really want the gaskets glued down to the block as that would make them harder to remove next time. I've re-used the original bolts after cleaning them, but I may use stainless steel studs next time. They can be had on ebay. I think I put Loctite on the bolts.
For a thermostat, I think I have a Stant. Stant has been purchased by Motorad in the mean-time, so Stant branded thermostats are not as common... on Rockauto at least. I'd probably buy a Motorad as I've used them in other vehicles. I do have a GM thermostat in my parts stash, should I need it.
Get some new Gates hoses if yours are older. I reccomend keeping the OEM constant tension band clamps. I'm not sure of they're availble from GM anymore.