I try and xyz summon with cyber dragon drei and cyber dragon core, I summon core first and then summon drei and use it's effect. i have many rank 5 xyz in my extra deck but it only lets me summon like half of them.

here's the replay: 

Cyber Dragon Drei
When this card is Normal Summoned: You can make all "Cyber Dragons" you currently control become Level 5. You cannot Special Summon any monsters during the turn you activate this effect, except Machine-Type monsters. If this card is banished: You can target 1 "Cyber Dragon" you control; it cannot be destroyed by battle or by card effects this turn. This card's name becomes "Cyber Dragon" while it is on the field or in the Graveyard.