This is a long shot but I had really bad intermittent stalling at highway
speeds, The well known Vanagon syndrome. I never got rid of it until I
tried a K&N air filter to get more power. The van has never missed again in
15000miles and 2 years of operation. The original air filter was clean, I
never did try and reinstall it to see if the bucking returned since I did
not want to tempt fate. If you try it and it works let me know.

Tony