With those mods OP you should be manically wheelspinning into oblivion if you're flat out in 1st and 2nd, i can't even pass 1/4 throttle in the damp/wet without spinning up.
When you say 'quick off the line' I hope you have DTC on, if you haven't pressed the DTC button, then traction control will be raining it all in and making it very 'normal' (often without flashing the tell tale light)
Try DTC short press (you can set the JB4 to automatically do that for you). I always run with DTC on, really takes the shackles off the motor.
Also remember oil has to be warm before JB4 will give higher than stock boost (you can set the JB4 to flash your dash indicator lamps to tell you when the oil is warm enough)
E63 AMG here at last!