Rear Differential Help with fluid shooting out vent hose.

Ok need some help. Have 14 bolt gm cab and chassis rear end under my 98 Dually. It came from 74 bread truck. Looked really clean inside changed fluid to synthetic up to fill plug and rolled on. Have about 1000 miles on it now under my truck. Had a short vent hose routed over the bridge and started to squirt out a good amount of fluid when going down hwy for about 10 or more miles. Talked to shop they said should make noise if bearings are bad. Gear wear looked normal. No noises at all. No play in pinion bearing. They told me to make sure not too full and route longer breather hose up in bedside higher and make sure cap flows free so don't build pressure and burst out fluid. Ok added 8ft hose all the way up to front bedside pocket inside bed. Checked fluid at fill plug and was 1/2 quart low. Still no noises and drove down highway from cold and poured fluid all inside bed floor after about 5 miles highway speed. Tried to upload pic of fluid but wouldn't upload. Anybody got any input what next? Thanks

This is how the tube was at first before longer one was added.

This is a pic of current location of vent and how much it leaked after less than 10 miles down highway and back.

ok so mine done the same thing when i first got it together.....with my 2 link when i ride real low the pinion angle is point down slightly and thats when mine puked out fluid....after it puked out prolly 3/4 of a quart it stopped....so i just left it 3/4 quart low and ive put atleast 10k miles on it and zero problems....not saying you should do that but i got tired of washing off fluid lol

Ya I thought about that but just confused why it went 800 miles with no puking whatsoever and then it has started every time I drive it. And I did just add 1/2 quart to it to top it off but that was just to see how low it was in case I was about empty. But have thought about taking more out to see cause it is a 2 link bar setup but barely angles forward any when down riding low but not sure if it will stop. Worth a try I guess. Thanks for the feedback for sure. And anyone else please chime in too if you know or have had similar experiences.