well, I'm not exactly sure why your hitting fuel cut...here is a hypothesis though...it may not be correct but it is an idea.
When you removed the lighter spring, it made the valve "lighter" and easier to push up...
my guess is that you are not recirculating the valve...if you are recirculating then my whole idea is not valid.
what could be happening is that at lower rpms the valve seals well also at low boost, because that single spring is very capable of holding the valve closed. However, under higher load ie. 5th gear...the boost is sustained longer...causing the spring to undergo the pressure for a longer time this could open the valve slightly just enough to leak boost.
if the bov leaks an amount of boost. the turbo has to work harder to maintain a certain boost level...so now, maybe the boost before the BOV is 21-22psi but after it, it is 19psi...your air meter would see 21-22psi of air-flow and cut fuel...even though only 19psi is getting to the engine...it doesn't know this.
ok thats a possiblity if you aren't recirculating the valve...which I would reccomend.
Now, about Vishnu...I say f*ck vishnu...personally I strongly dislike them...they seem to be more liked in the Evo community but I would NEVER go to them. They are only in the business for money...thats all they care about, and they are a rip off...and they don't even do that good of a job at what they do. Sh*t, vishnu doesn't even install their parts, the shop right next to them does...and they both charge bitchloads for everything.
Since I have tuning experience, I know I could do a better job then vishnu could...I personally have to take some time to learn the AFC...but I know I will be able to tune mine quite well...
Also I said vishnu is only in it for the money...well, yes other shops are too... but if you call and you talk to people like Buschur, DSS, RRE, RnR...etc...those guys are really nice and actually spend some time to help you...I'm kinda baised with DSS, cause I know Mike personally...but seriously he is on the phone everytime I'm there and it seems everytime that somebody will call him with a tech question and he will take his time to help that person...I'd like to see Shiv help a DSM'r out...
They seem to "like" Evo's better...but just because of their attitudes, I wouldn't bother or waste my money with them... If you need help tuning your with your AFC, and you have gauges and proper things to monitor stuff, I'd love to help you...though I'm a good 5 hours south of you...I'm sure if you took it to another shop, like DSS (also 5 hours south
) that Mike would do a better job than Vishnu...and charge you less...
But I still got my dsm 
