I knocked out a 135 rex in the snow biome it was stuck at a place i started to feed it its torpor was full according to dododex it didnt needed any narcotics i died after like 5 mins i came back and it was roaming free i was sooooooo mad that i killed it so THANKS DODODEX!!!!!
If you use the bear trap strategy which is if you lead it into a Dino gateway that is shaped in a triangle and with a bear trap in the middle (Large Beartrap) and when it is stuck you must put a dinogate behind it to trap it and then knock out. (hope this helped and "If" I win could it be an Xbox voucher, thanks.)
Create a 3x3 mobile taming pen 3 walls high on a raft with a Dino gateway on one side and ramps on the other. Use a flyer to lead it up the ramp into the pen then move it to a safe area to tame. I got 2 150s without a single issue.