I recently had my auto transmission oil changed with a AT specialist recently and he advised me to try and drive in Sports(S) mode most of the time and in particular whilst towing to prolong the life of the AT. This takes away the gear hunting problem, but he also described how the gear box changes gears differently between 1 to 3rd and 4th to 6th when in drive(D) and sport(S). He also showed me the solenoids from a gearbox he was working on and explained how problems can arise with them and why, and what to look out for (or feel) when driving. Interesting bloke who actually spent some time to explain these things to me and show me around his workshop.