Its is still recommended to use the top and bottom inserts. I believe the spring you are refering to is the reverse return spring. And yes it is a little stiff right now but like you said, I am sure it will get better with time.
2012 GT 5.0 Ingot Silver
6M,401A, RR sensing sys/security pkg.,19" painted alum wheels,GT coupe accessory Pkg 5, Ford Racing SVT Sport axle-back mufflers w/o resonators, MGW shifter, Airaid cai/Steeda 93 tune, Boss quad exhaust.