I have a 2000 EX and its the same as yours. There is no need to add anything to the rear suspension. It trailers just fine as built. At your mileage it probably needs ball joints and a front steering stabilizer replacement. The stabilizer made by Monroe is the way o go. Two very important things to check...first is the rear differential cover as prior to 07 Ford had a problem with them rusting through. Mine did and I lost the rear end. Second is the rear brake line mounted to the differential housing. Look at the top of the gear housing...the line is snapped into a clip. When they did this it scored the coating and the lines rust through at that point. As for other items. As a long time old school mechanic I have never been a proponent of all this changing of fluids unless needed. Ford uses full synthetic in the diffs (different in fron and rear though)...should be good for many more miles. Unless the trans fluid is starting to burn it should be ok. Spark plugs will be good for many more miles. However the weak point is the coil on each plug. You can get replacements for as little as 10 bucks today online. I always have a spare and a 6mm nut driver in the glovebox just in case....and was glad I did twice. I run my Ex in stock form towing a 35' 10,000 lb trailer all day long at 65 to 70 mph with no sway or problems. Up north average 7.5 mpg and south of VA about 9mpg. South of VA also get to use overdrive a lot.
