For the record, fuel trucks slow the departures of the ai traffic. Because once an ai plane calls for a fuel truck it CANNOT leave until it has been fueled. FSX does not really allow the use of mulitple fuel trucks, they do but they have to each be working a specific area. Sometimes I have called for a fuel truck and I was number 7 in line, and that takes a good amount of time for it to make its way over to me. I have found that the ai flows more smoothly if there are no fuel trucks.
Just my opinion. Thought I would share it.