Hey all. So getting my Van ready to sell, and I'm having an issue where there is a extremely loud squeal from the motor area.

It only squeals as you add throttle, and the vehicle won't go above 30 miles an hour.

The squeal is coming from the rear right of motor,, near the transmission..

Oil is good, transmission fluid is good.

Squeal coming from this area.

 

Possibilities include restricted catlytic converter/exhaust, transmission issue if the engine is revving due to slippage.
I don't believe even a severe vacuum leak is going to limit your speed to 30 mph.

 

Something you can try,
when the engine is idling, place your hand over the outlet of the exhaust pipe.
You should feel steady pressure, if it is restricted you won't feel too much.
The tech way is to connect a vacuum gauge and watch the vacuum reading while raising the engine speed . If it continues to drop that would confirm a restricted exhaust.