Has anyone experienced the following problem on their GL?

     During a recent trip from Virgina to Florida (1100mi) our 84 Vanagon GL
worked perfect on the interstate, but when we hit stop-n-go traffic in small
towns on the second day, we could not take off in first. (reverse would not
work either) The Van would buck severely (it felt like the engine was going
to fall out ) as if you were trying to start off in 4th gear.  When we got to
Florida (after driving the last 400 mi not using 1st gear) and took the car
to a mechanic the following day, the Van worked perfectly.  On the return
trip, everything went fine until late the second day when the same symptoms
occurred.     
     The day after we arrived home the problem disappeared.  We are planning
several long trips this summer to see family and do not want to experience
this again or worse yet, get stranded.  Any feedback or suggestions would be
helpful.

janet and drew
84 GL  
220K
Virginia