Sounds like over boosting which mine did and i returned the box for not a full refund. I bet if you scan it with vcds you'll have an engine error relating to over boost.
Do you mind me asking Chris how much he deducted from the refund.
I don't remember seeing it mentioned on the DTUK website that this problem occurs and how often. I wonder why.
I tried driving without the pedal box last weekend and it felt very similar to limp mode today, felt really sluggish.
Thank you again for it Chris.