astro van 1999 4.3 vortec v6

What is your question?

van runs good on flat roads when i go up hills and it shifts into over drive van shakes and engine light flashes and then goes steady, as specialy on hiway, i go light on gas never does this .???

What makes this problem better or worse?

its better light on gas all around its great.

How long has your 1999 Chevrolet Astro had this problem?

4 years