You should always consult your owner's manual
as many manuals recommend that you service your vehicle
more frequently if you drive in "severe" conditions.
Any of the following qualify as severe conditions: driving
in stop-and-go traffic, frequent short trips, extreme hot
or cold conditions / temperatures, towing and hauling, driving
at prolonged high speeds, frequent start-ups and shut-downs
of the ignition, extensive idling, or driving in mountainous
terrain.
To avoid transmission problems, the Automatic
Transmission Rebuilders Association (ATRA) advises in its
consumer bulletins that customers should be aware that driving
their auto, truck or SUV under "severe" conditions as listed
in the Owner's Manual can cause extra wear and tear on the
transmission. For instance, relatively low mileage transmissions
that are regularly used in city or stop and go conditions
are subject to much higher wear than transmissions of the
same mileage that are used under normal or primarily highway
conditions. It is important to note that it is not necessarily
the mileage on a transmission which determines probable
wear and a greater probability of your auto, truck or SUV
needing a transmission repair. Rather, it is the number
of times the transmission has been run through its start-up
and shift cycles that determines probable wear.
Many other seemingly normal driving conditions
can effect transmission life and a higher incidence of repair.
Things like extreme climate conditions (either cold or hot),
mountainous driving, motoring problems which are associated
with snow or ice and slippery conditions (and a host of
other conditions) can take their toll and cause more frequent
need for repair.
As you can see from the limited examples
above, many motorists do not fit into the ideal or 'normal'
driving condition category. If you operate your vehicle
under more extreme conditions, servicing your transmission
yearly seems to be an industry average. Under the most extreme
conditions, it may be advisable to service your transmission
even more often and you may also want to install an external
transmission cooler for additional protection.