I'm a Ranger/Cleric who wields a two handed weapon. Do I need the why caster feat? I've seen conflicting info.

 No you don't. The Two-Handed trait says;

This weapon requires two hands when you attack with it. This property is relevant only when you attack with the weapon, not when you simply hold it.

So it is fine to hold/carry a two-handed weapon in just one hand, you only need to actually use both hands when you make the attack.

Changing grips on a weapon does not require any kind of item interaction. Two handed/versatile weapons are cool like that.

You can be wielding a 2h weapon, take 1 hand off to perform somatic components of a spell then resume your grip, no problem.

Warcaster feat might still be useful for a melee spellcaster though. If not for the ability to perform somatic components while holding weapons, than for the advantage on concentration and casting spells as opportunity attacks.