E-350 vs. 3500 promaster

If the Promasters are still using their "clutchless manual" transmission I would stay away. There's a huge pause in acceleration every time it shifts. Since you don't know exactly when it's coming like you do in an actual manual transmission you are pushed forward off the back of the seat by momentum during the shift. I found it extremely annoying on a test drive. Maybe after owning one you could be able to anticipate the shifts and not bob forward every time.
Also, I thought the Promaster had poor side visibility. The B pillar is too far forward.