Back when I had a shackle only for a week...
I would suggest ANY name brand, belltech, DJM, Eibach.... Just get the ones that come with a shim. You might need a shim to get rid of driveline vibrations, you might not need it, but using it regardless wont hurt it. Simple to install, hardest part is getting the truck high up in the air enough to let the suspension droop.
There is a vendor on here, go to this thread and tell him you want a shackle, he haas the absolute best prices.