I disagree with almost all of the above posts depending on how much effort you are able to SAFELY provide. Dropping the pan requires certain tools (jack and jackstands) to do it safely while using a vacuum pump can be performed under the hood. It all depends on your own circumstances and skill level.
A Ford ATF filter is a "lifetime" filter which only captures very large debris, but changing some of the ATF to "fresh" fluid can help your overheating more.
SPK2000:
Your 1998 Mercury Marquis 4.6L 8-cylinder has transmission 4R70W.
If you drop the pan it will drain between 4-5 quarts (assuming you have the correct level now).
You should be able to remove nearly this much with a vacuum pump and it is much easier to use the pump.
You can drive around for a few days and then vacuum out again and add more new ATF and this will give you a good "refresh".
If you perform a complete flush including the Torque Converter, then the total capacity of your transmission is:
Automatic Transmission, Total Fill
4 speed 4R70W..........
13.9 quarts
Wal-Mart has a great ATF for $18/gallon (4-qts) called Valvoline Max-Life...it is a full synthetic and it is compatible with your current fluid:
https://www.walmart.com/ip/Valvoline-Max...13=&veh=sem
If you decide to change the Trans Filter then here is a good kit:
https://www.summitracing.com/parts/wix-58955