98 4.3 Blazer leaks trans fluid out of vent tubei

1998 blazer with 4.3 4x4 automatic with 120k miles, there is a breather tube coming up in the rear of the motor with a vent cap like on a differential and trans fluid is coming out of it at higher speeds like 2000rpm, I just traced the hose to the top of transfer case and it is mated with 2 other hoses 1 goes to pvc port and has vacume, and the other went under the battery, do you know why I would get oil out of this breather tube, I just got the truck and the owner said they changed trans fluid and filter, I am stumped
thanks, Dan