Re: trouble tighening harness tension
Both the SKJP Radian and the TrueFit have ratcheting adjusters, so you need to tug release tug release. If you have a Diono Radian (the ones that have booster mode) then it's a smooth adjuster. Regardless of the type of adjuster, I always tighten like this: grab the harness just above the crotch buckle and pull up to get any slack out of the hip area. Then reach behind the seat, and pull the harness there to pull the slack out of the chest/shoulder area. Then you can pull the harness adjuster to get the slack out of the back of the seat.
The TrueFit's harness is one long strap that goes from the splitter plate in back, through the shell, through the chest clip and crotch buckle, down under the shell near the child's hip, then comes up by the other hip, back through the crotch buckle and chest clip, through the shell then back to the splitter plate. To even it out, grab the harness near the child's hip on the tighter side and pull up a bit.