So I have had my new Fast LSXRT intake on my 5.3 Silverado for two weeks now and cant seem to get the tune ironed out completely. Let me start by saying I have long tube headers, off road y pipe, AIRRAID intake tube, and a home ported factory 87mm throttle body. I can get my steady state VE good, but the tip in and tip out fuel trim is totally jacked up!! I have tried at least 75 different approaches and nothing will fix the problem. I finally discovered something last night in my late online searches. The VMAX Velocity Ring!! It seems that the transition from the 87mm opening on the back of the throttle body to the 102mm opening on the Fast LSXRT intake is causing the air to stall and create these lean tip in issues. Now if you have the ability to make north of 550 to 600 hp then obviously you will have a 102mm throttle body and this will not apply to you. But if you will be using a stock 87mm or 92mm LS3 throttle body then you will most likely need to purchase one of these to get the natural tip in that your vehicle had with the stock intake. I felt the need to post this up as I see tons of old threads about how people that have had problems tuning these intakes as I myself did. After calling FAST about the problem and them telling me that the intake doesnt require any tuning, I knew this was gonna be an uphill battle! The owner of VMAX returned my phone call on a Sunday morning and spent an hour on the phone with me explaining and educating me further on the subject. I truly hope that this information is found by people that purchase this intake only to find that they have driveability issues that would not iron out in manipulation of the tuning. I should also add that I feel my ported throttle body is probably aggravating the situation as well. I am going to put on a stock (unported) LS3 throttle body on so I can scavenge on the better flow without taking the lip out of the throttle body this time. Here is a link to the product. http://vmaxmotorsports.com/?p=192