Any codes on the Scanguage ? Could be what we call ¡®limp¡¯ mode. This happens when a transmission gets too hot or if some solenoids around the valve body are defect. The van, then, starts shaking and hesitate. You¡¯re finally into 3rd gear only. The trick is to stop the van for almost 2-5 minutes, then restart it to see if everything¡¯s fine again !!! It once happened to me... Do you have? a transmission cooler installed ?