Increasing the resolution in RMXP can cause lag. Blizz-ABS is a system that already adds a certain amount of additional processing to the game. If you increase the resolution on top of that, the game can become unplayable. I'd actually rather recommend you don't use an increased resolution at all.
You should be able to fix the problem by changing the viewports in class Spriteset_Map.
Also, if you did that with Sprite_Character, you have completely messed up the system internally. The system now doesn't know anymore how to handle sprites through the anti-lag system and won't allow any kind of advanced sprite usage like sprite animations. Are you sure you want to abandon all sprite animation capabilities in Blizz-ABS just for a higher (and more laggy) resolution?