What is the chance that I will need to have my transmission repaired?

I have a 1997 Ford Ranger automatic 6 cyl 3.0 engine. The truck has had the transmission fluid dropped and a new filter added every 6 months up until this year. In which , the truck has only been driven around my development and to the store a couple of times. Being I will be returning soon maintenance will need to be done ,but I am worried. I have been told by the relative that has been taking care of the truck that she has not noticed any problems. The truck has about an 120,000 miles on it. Am I getting nervous for nothing?