To service or not to service transmission
 

Hey all, 2004 FX4 4.0L 4x4 auto trans w/ 185k miles here. Got it about a month ago, so previous service is entirely unknown.
Should I or should I not get my transmission serviced?
It shifts fine, maybe a not-so-smooth shift every once in a while, but nothing really concerning. I know it can definitely be a lot worse.
I know that getting it serviced can lead to issues that weren't there beforehand, so is it a bad idea?
I know these transmissions aren't that great, and I plan on having this truck for a while and building it into an overlander, so I want to keep the transmission in good condition, and I would rather pay for a $200 service now than a $1000 repair later.
Is that a bad idea since its not shifting bad yet?

I am not a transmission expert but I would service it. I had mine serviced around 150k when I got it and it's been fine and I tow quite a bit with it. It made 1 weird shift when I was leaving the mechanics shop right after the service. Nothing weird since and I'm About to cross 190k

I read that MYTH all the time
Changing the oil in the engine OR transmission is required not optional

If you wait too long then damage was done by the OLD oil, not by putting in new oil
So any "perceived" issues after servicing was from damage done by waiting too long, for sure

Almost everyone that has major problems with their transmissions after getting it flushed,
had problems before getting it flushed and were hoping that flushing it would FIX the problem.

I would at least do a drain & fill & change the filter.

If truely leary of a full setvice drain + new filter + new gasket + several quarts of new ATF, you can just hand pump a quart of the old ATF up thru the tranny diptube, then refill with a fresh quart of new MerconV. I do this every 5kMiles 6mths to keep tranny happy between full service 33kMile 4yr intervals. This would be the absolute least that you should do.