I thought I was having major transfer case or wheel speed sensor troubles on my '02 EB because of on any situation that required the application of power, the 4WD would kick in at any speed. Had a major issue with the dealer over all of this and they couldn't figure out the cause and wanted to replace the clutch packs in the front transfer case and the wheel speed sensors after changing out the front end's fluids. Come to find out that it was all because of the treadwear differences between the front and rear wheels. I replaced my quite worn rear tires with a set of Michelin X's that had almost identical treadwear to my front Cooper's (a bit more than half tread). Problem solved immediately. It seems that the onboard computer senses wheel speed very carefully so that much difference between tires cause it to think a wheel slippage is occurring and thus the 4WD kicks in to fix or in this case exaccerbate the problem. Per my '00 Toyota 4Runner's recommendations from the factory, I'll be rotating the Explorers in the diagonal pattern to hopefully keep the treadwear even.
As an aside, the Michelin X's that I'd put on when new were well over $200 each and the the used ones mounted, balanced, new valve stems & etc. cost me a grand total of $52.50 tax and all for the two of them. I may not ever buy new tires again after running across this local used tire dealership that does stand behind them. They have a network where they can get almost any brand and size for incredibly reasonable prices with a little notice. They get them of recent totals and also from the folks that upgrade wheels and tires. The guy that owns the used tire place makes more money on his great used tires than the average new tire dealer does. The tires that I bought for basically $26 each have at least 25k miles left on them!