I have 150,000 miles on my 2000 Explorer, which I purchased
new.  My other car was recently totaled, and I'm considering
replacing it with a 1999 Explorer with 75,000 miles on it,
thus becoming a 2-Explorer household.  The 1999 belongs to a
friend, and I have ridden in it many times.  Inside it seems
pretty much the same as my 2000, and I wonder what are the
significant mechanical differences between the two?  The
1999 has 4-wheel drive, whereas my 2000 has 2-wheel drive,
so that is a major mechanical difference.  Any others I
should know about?

Many thanks.