Sometimes trannys get finicky like that and giving it gas and letting off gets it too shift. There is a vacuum controlled solenoid on some trannys and around your year of van electroic solenoids were also used. Since they tried re-setting the ECU, I am guessing it is electronic. There is some input from the throttle position senor. So, you can, "Train" it to possibly sift a little better by being more agressive with the thrttle when getting ready to shift into that gear.
I think if there were contamaination or burnt fluid in the tranny, a dealership would probably tell you. So, as long as it does not feel like it is sliping when in gear, just look at fluid every so often to make sure it does not look, "Burmt or Brown". Look at it now to see what it looks like, usually red in cvolor, but just so you know what it looks like when fresh.
I hope this info has helped.
Wednesday, September 21st, 2011 AT 2:32 PM