Hissing coming from under my ford 2e250?

Hissing sound coming from my ford e250? There's a disconnected hose right under the passenger side, underneath. It has 3 holes and stops when I out my finder over then. What could it be?

1988 Ford E-150 Conversion Van Road trip checklist?

I have a 88 Ford E150 with around 89K original miles. I live in Atlanta GA, and I'm going to Nashville TN for Thanksgiving. And instead of renting a car, we re taking the Ford. It runs pretty good, as it is my daily driver, an hour to work and an hour back. The radiator needs replacing. So I have already purchased that brand new from AutoZone. Also the steering wheel is tilted to the left and it drives that way. I'm sure that it needs a front end alignment and new tires. Today, I turned the radio off and I rolled down the windows and I drove the van on the expressway so I could listen for noises, and I was very careful as I was looking for smells, noises or anything awkward. And I didn't notice anything. The van drove smoothly and it shifted well. My gas mileage is terrible. The van was my father s. It only sat up for about 6 months after dad died. I really don't know the mechanic/repair history of the van. After those 6 months, I got in it and began driving everywhere. I've been extremely lucky, because apparently dad took care of the van, as the only problem I've had in it was a tire blowout. And all of this has been within the past year. I'm going to go ahead and begin with the basic things to get them out of the way. Such as purchasing a brand new set of tires, replacing the battery, doing the brakes; make sure that the headlights & tail lights are working. But I'm sure there's more. So where do I go from there? Please advise with a road trip checklist.

My van slip only at 30km?

I have ford freestar 2005 and each time it reach 30km, I feel suddenly boom like transmission slip somewhere and this happen each time.
Thé fluid Is flushed and level ok,
There was recall for torque converter and it was changed also.
Someone say On youtube for this kind of can the reason for slipping is pump shafts.
But I'm not agree because the slip happen only at 30km not before or after.