Re: surging at 4-5K (trbogolf)
It might be your DV valve or a boost leak. If anyone near you has a VAG COM hook your car to that and see if you get any codes.
also check the search feature on "surging" there should be plenty of posts about it. I myself have had surging problems with GIAC. See if you have the latest version of their software.
good luck,
James