need some esc advise please...

[DwightSchrute]

i'm running an mmp with the castle 2400kv sct motor a castle caps bank on the esc. usually i run it on 3 or 4s and it does great. today for shits and giggles, i decided to put 5s in it and see what it had. (this is all in my slash 4x4) I'm also running 40C 5000mah packs

when i squeezed the trigger, it crawled. then all of the sudden it comes alive and drives perfectly. then it does the same thing. i pull the trigger and it barely rolls...then i start feathering the throttle a bit and it seems to get it's ass back.

any one know what this is? like i said, it's perfect on 4S, but the 5S was really acting funny. could it be i was overgeared or something? any help is appreciated. thanks