Re: 1999 explorer
The TCCM is probably your culprit here. I'm guessing you have electronically controlled T-case (buttons on dash). If that's the case, the TCCM should be located under and behind the dash on the right side of the gas pedal. It's not a cheap thing to fix, even if you do it yourself as a good part at a salvage yard can easily run $150-200. A new TCCM will set you back twice that at the dealer - plus installation if you so choose.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!