Wow!! normally the T/C sights.. while I personally do not like them, are pretty good as far as being set. I have all my Renegades set half and half on the back sight and they hit dead on at 50 yards.
I hate to recommend a new sight. I would clean the guts of the old back sight, first. There is a spring in there. Still ... because it is shooting high, with the sight all the way back, there is no where else to go.
Check the screws in the rear sight and make sure they are good and tight inside, under the cover of the rear sight. Be careful when you open that, there is a spring in there that likes to disappear faster then a plate of brownies at a weight watchers meeting.