Did you check the frame again after hanging the doors? Could be that the frame wasn't securely attached to the studs and the weight of the doors is causing the frame to pull out slightly.
Also, maybe too late for this now, but you mentioned that the old frame was about an inch wider than the new one. That seems a bit strange. Is that the rough in dimensions, or the finished frame dimensions? Usually the rough in is a couple inches or so wider than the actual door frame dimensions to give you some room to plumb things up with shims.
So if you had a 48" door set, the rough in width would be 50" - 48 for the door, 1 more for the frame, and 1 more for shimming.
I had basically the same situation in my 70's-built house, the closet doors went all the way to the roof, and were horrible looking bi-folds.
![before](https://i.stack.imgur.com/ECnNSl.jpg)
Basically what I did is framed in a header to bring the opening to 81" (remember to account for 1/2" drywall while framing):
![new framing](https://i.stack.imgur.com/yYbwVl.jpg)
Then some drywall and paint (note I didn't yet repaint the ceiling in this picture):
![drywall complete](https://i.stack.imgur.com/JhKoll.jpg)
I had 4 closets like this. One by the front door got sliding mirror doors, the rest got frosted-glass sliding doors. The right picture below is actually the "after" shot of the first one in this answer.
![finished with frosted glass doors](https://i.stack.imgur.com/Hle7km.jpg)
The width is going to be challenging for stock stuff. If it was a bit wider, you could probably split the door into two by putting a small column in the middle, but that would leave you with a couple 3.5' doors, which are pretty small. If you went to bi-folds, you might be able to do a 4' and a 2' door, though that might look a bit strange.
A quick search turns up some custom closet door manufacturers, which might be an option to get multi-panel sliding doors, like this:
![alt text](https://i.stack.imgur.com/ntVsV.jpg)
If you do this you can probably also get them 8' high, but honestly, even without the doors on, just making the opening 81" really updated the look of the house.
Yet another option is that you could shrink the width down to 72" (basically just extend the wall/framing on one side by 9"), and along with making the height 81", you're into a standard size where you can get both sliding or bi-fold doors off the shelf from any box store.
Good luck, and let us know how it turns out
Best Answer
You want the doors to overlap a bit. You also want the two doors to be the same width so when they are slid all the way to one side or the other that they are even.
A one inch overlap is about ideal so for a 48" finished opening each door would be 24.5 inches wide.
Two 24" doors would not overlap at all and would not stay fully engaged into the center guide on the floor.
Doors wider than 24.5" would work just fine but you loose access width when the doors are open.
My suggestion is that you may want to look at bi-fold doors. These would take four ~12" wide door panels. They work with one track at the top and eliminate the center guide on the floor. When open you get much much easier access to the closet than with bypass doors. Plus when closed the whole surface is flat. The only time I consider bypass doors is when mirrored doors are used to give a smaller room a more expansive look.