Hey guys, So I just purchased a brand new 2015 15" Macbook Pro (the $2,000 base model), however when I hook it up to my new Dell 27" 4k Monitor, Photoshop become very laggy. If I try and use the brush tool, it takes second to register my strokes with my Wacom Intuos Pro. I have the resolution on the monitor set to 2560x1440 (same as the Thunderbolt display). Is there a reason why this is happening? Thanks for any help.