What year van? I had a 97 with the 5.9L and 46RE transmission. unless its a very early 90`s 4 speed they are pretty reliable transmissions. I think the 5.2L may have had the 44RE.
with that said, there are far more things to be concerned with. rust! brake lines and fuel lines. inspect the area around the steering box good. they tend to rust around there badly to the point the gear box will come loose. everything else is dependent on how it was taken care of.