Transmission fluid change intervals

I have a 1999 Villager with 90,000 miles. Runs great, but wondering how often to change trans. fluid? The manual just says "inspect" at certain intervals, but never "replace." I purchased the van at 60K miles and I've never had any trans. problems. Since the fluid looks and smells fine, too, it may have been changed at least once since new I am assuming. I am asking because I want to pull a pop-up camper some this summer and want to avoid any problems. Some say it may make things worse if you change it too much, so I wasn't sure what to do.

Wow, this was my first foray in this forum. I am quite surprised no one could answer what I thought to be a fundamental question. Oh well...

Look at it this way, if its broke fix it. If its not well you know. I would have to say every 30 to 60k. The manual is right check it if it looks darker or burnt change it. Don't go changing things based on previous car experience. This van it tough and it has its own issues that you will need to deal with down the line.

PS SORRY FOR THE DELAY IN ANSWERING YOUR QUESTION.

Thank you!