The usual failure for that truck is transmission failure. They’re “sealed for life” types, so you theoretically can’t change the transmission fluid.....
The 3.0L V6 was a bit questionable, but the 4.0 (which I think they were using by 2000) is a pretty good engine. They also had the old 302ci/5.0L V8 in them in that era.
Except that fluid changes are specified in the owner’s manual.
The lack of a plug doesn’t mean you can’t or shouldn’t change the transmission fluid. Ford was having so many failures that were directly attributable to improper maintenance that they removed the plug? “What?”, you say?
The fools at the quick lube places were mistakenly draining transmission fluid instead of oil, then not refilling it. Running a transmission like that will kill it in no time, regardless of make. Ford’s response was to remove drain plugs (cheaper to manufacture as well). It makes the fluid change a pain, of course, but it stopped a huge % of the transmission failures they were seeing.