Typically it is caused by old rubber lines that closed up, just like our arteries! However if you replaced them within the year they should be ok. Are they dragging to the point where the rotor hat is hot? Maybe your parking brake adjustment on that side is too tight or stuck? How did you set up the bearings?
Since there are some unknowns, what I would do is get the car in the air, disconnect the 1/2 shaft so you only have the caliper, bearings, and parking brake in the equation now. If it feel tight at that point, remove the caliper and see. These bearings can be setup in a preload, which is how you build a Tom's axle set. In stock form I set them for -0- lateral play. You will hear everyone telling you to set them at 002 but few- VERY few, truly understand this. If you used a set up tool and set the bearings for say 002" endplay on it and get it assembled and find 005-006 the bearings were not set up correctly. Now this would be opposite of what you are experiencing but I threw it out there to check. At -0- lateral play they will still have 0015 endplay in them. They will rotate smooth but have no play in them.
Next the parking brakes. If you used new SS parking brakes and just installed them then you might have an issue with them. ALL new SS parking brake kits come from only a few suppliers, some have LS stamped on them from Lone Star, others do not. Regardless I have to fit every single one of them and have had to for the past 10 years. The hold down pins are stamped and since it takes time to clean them up the mfg just packages them. The problem is they are not sharp like an arrowhead and do not fit correctly in the spring cups. They can pop apart later on. Next the star wheels are always too long. I now face everyone 090" in a lathe, I don't bother checking new ones because I know they are too long. If you put together the brakes and noticed a tickling noise with the star wheel fully compressed then the shoes are dragging and will get hot. Another part not addressed in these kits the levers. They have sharp corners on one side that I found sometimes hit the upper shoe spring and pop it out. The trick is to radius the lever to prevent this. YET NOT ONE VENDOR WILL TELL THEIR CUSTOMERS ABOUT THIS. Notice some vendor frustration here? Some with the diff rebuild kits sold for 63-66's no once tells their customers the shims in the kit are useless, yet they are sold everyday.
The brake system is pretty simple, you will find the problem once you look, hopefully it's minor. Another thing, DOT3 fluid is good but if it absorbs moisture it becomes an acidic mud. SS calipers only protect against wall pitting but the mud will clog up and pistons can lock on and drag. I had it happen to me years ago.
