Re: trouble tighening harness tension
The Truefit has a continuous harness, which means that the sides can get uneven. I would even them out without a child in the car and then readjust as necessary.
The Radian harness adjuster can be a pain in the neck, don't even get me started.... ours ranges from difficult to nearly impossible. It might help you to know that the mechanism is designed to work in a ratcheting motion, so it's tug-tug-tug rather than one smooth pull. Assuming the seat is rear facing, it might help to pull the excess slack from the back side of the seat with one hand and then pull the harness adjuster strap with the other hand.