(I've only tested this out on mobile, idk if it works on pc!) If your Giga rages, you can end the rage by doing this: Put your device to sleep, and join into ark again. The giga should be calm again! I once fell off a ledge with my Giga, Giggy, and she raged. I reset my ipad to calm down, and when i came back, Giggy was calm and mountable again! Giggy is fine now btw. I had been planning to turn invulnrability on, but i looked around and Giggy was calm. I hope this helped you and your raging Giga!
I triple dog dare you to tame 2 EXTREMELY high level gigas (When I mean extreme I mean around 200-250, or above) and breed them you'll come out with a freakin' bulldozer that can go toe to toe with the dragon boss, ALONE.