Important to mention that you have 2 gearing options from the factory on the 02-05.
It's easy to tell which one the truck is equipped with (without referencing the axle code on the VIN). If it has the 1.5" square hitch receiver (Class II), you have the 3.55 gearing, if you have the 2" square hitch receiver (Class III) you have the 3.73 gearing (D4 axle code).
With you planning to do some towing and maybe some 4x4, I'd definitely look for an Explorer with the 2" receiver not only for the included towing package, but also for the 3.73 gearing which is much friendlier for 4x4 and towing a camper/family.
As mentioned above, the 2002's are notorious for having problems...more than the 03-05's. There were some changes in each year, ranging from mechanical improvements to cosmetic (exterior and interior) changes...as subtle as they may be.
I'd stick with an '03+, stay with the 4.0L which is a strong motor, go for the D4 axle code (3.73 gears) which has the towing package, and have it inspected by a trusty mechanic whom you know.
Also, if you know someone in the Ford Service dept industry, get an OASIS report pulled for the truck. It's Ford's internal service department database, which shows everything the truck was serviced for, including recalls, TSB's, warranty service, and scheduled maintenance. These aren't things that show up on a CARFAX.
I can assist you with the OASIS if needed...but I'd need to have a VIN...and the OASIS thing is a little hush hush around here. I personally cannot get them, but I have a guy in the biz who can
