Why is my dryer squealing even after roller replacement and lubrication?

Were the shafts clean? On dryers that I have replaced rollers there has been residue from the original roller. This residue increases the friction and may be the cause of your noise , the rollers I have replaced did not have bearings but were like a dense plastic with graphite impregnated they were not supposed to be lubricated if you have similar you might try cleaning with some isopropyl it sounds funny but a lubricant may cause problems in this application, if a lube is needed a grease would be more appropriate.

1. As mentioned, check the roller shafts. Not only must they be clean, but any burr or nick can cause increased wear. Most shafts can be replaced in seconds by removing a single nut. Also verify that the shaft and roller are correctly assembled, with no missing or extra hardware.
2. Check dryer level and cabinet orthogonality. If the cabinet is untrue, or tilted (e.g. because a rubber foot fell off when moving the dryer), unnecessary strain is put on one pulley.
3. Check also the idler pulley, which is part of the belt tensioner. Again, if replacing the pulley, also replace the shaft or the whole arm -- the difference in price is slight, and the effort to service far outweighs the cost.