Luxurious Lincolns are nothing new, but a leather-lined machine that brings together the ambience of a Continental with cavernous load-carrying space and go-anywhere ability was sure to cause a splash. And that's what the Lincoln Navigator has done. Sales are increasing at a pace that has seen the big Lincoln sport-utility surpass the Continental in popularity and edge steadily closer to the nameplate's leading model, the Town Car. The Navigator's success has three primary elements. It has all the requisites to appeal to buyers looking to be part of the SUV trend, including the high seating position, brawny looks and roomy cabin for passengers and cargo. To these it adds a host of features that coddle its occupants in a quiet, soft environment. Last, it is built on the rugged structure of the Ford F-150, the best-selling truck in the U.S. Good as it was right from the start, the Navigator has received substantial improvements for 1999, although the most noticeable of these, a new standard powerplant, won't appear until midway through the model year. Even in early-'99 form, however, Lincoln's off-road limousine makes a big impression in every respect.