Well I will be the first one to come on and say, I too had ALOT of tweak issuse with my car when I first built it.
But after sitting down with it for a few hours after the first build. I have gotten the car to not tweak at all....
It has been ran for two race weekends and I have not had the first tweak from it since.
What I found was that I just needed to undo all the screws top and bottom and make sure that the Bulkheads were square from the beginning. I found out that they were twisted during the first build.
To figure this out I measured from the edge of the chassis to the inside and outside of each bulkhead, front middle and back of each. Once I got them all square and Tight... No more tweak issuses for me...
Hope this helps out someone else..