From the owner's manual for the 2001 Ford Explorer, page 167: https://www.fordservicecontent.com/Ford_Content/Catalog/owner_information/2001-Expl-version-2_om_E

From the owner's manual for the 2001 Ford Explorer, page 167: https://www.fordservicecontent.com/Ford_Content/Catalog/owner_information/2001-Expl-version-2_om_EN-US_06_2000.pdf https://www.fordservicecontent.com/Ford_Content/Catalog/owne... >Use 2 (Second) to start-up on slippery roads or to provide additional engine braking on downgrades. >Use 1 (First) to provide maximum engine braking on steep downgrades. The weak point is the engine, not the transmission. If you're at 7,000 in fourth gear, and you command a shift to 1st gear, it will grenade your crankshaft. Some transmission control modules are smart enough to refuse to do this.