I just read that you did the "spring mod" and THAT was supposed to help with the "boost cut." That spring mod is helping the ignition which has nothing to do with fuel.
With the this boost/fuel cut coming it at mainly cold temps, it sounds exactly like the MAF pegging problem that can plague modified Lightnings and Cobras that do not upgrade their MAFs or tune to extend its range. This actually could be what is happening to the MS3 and is something the Cobb AP could fix if it is capable of tuning that parameter.
I see the MAP clamp helping trick the computer in to providing more fuel in higher boost and this preventing this "cut" and I can see a better pump helping prevent this as well, but if it is something like the MAF pegging then tuning and eventually an MAF upgrade would do wonders and then the big turbos, etc that could use the fuel system upgrades could come online.
I am not questioning the need for a pump with your mods since I don't have any idea as to what the stock pump's limits really are and have seen not hard data on that so please don't misunderstand where I am coming from. I am just thinking out loud...
But the "spring mod" helps with spark, so if that solved your problem, then we need to look at other things...