If I am leveling my 5th level Kineticist into a 6th level Kineticist, can I pick up a 3rd level Utility Wild Talent and then immediately trade it out for a 3rd level Infusion Wild Talent?
At 6th, 10th, and 16th levels, a kineticist can replace one of her utility wild talents with another wild talent of the same level or lower. She can't replace a wild talent that she used to qualify for another of her wild talents.
No. The replacements for levels 6, 10, and 16 are for utility talents.
To replace infusions, "At 5th, 11th, and 17th levels, a kineticist can replace one of her infusions with another infusion of the same effective spell level or lower. She can't replace an infusion that she used to qualify for another of her wild talents."