The 1980 episode of Dallas that revealed who shot J.R. Ewing drew 90 million viewers and at the time was the highest-rated telecast ever broadcast. When the series returned on TNT Wednesday night with all-new episodes it drew 6.9 million viewers -- tiny compared with the number of viewers who routinely watched Dallas in that bygone era, but the biggest audience for the premiere of any regular cable series this year and bigger than anything that aired on broadcast television the same night, including Fox's hit So You Think You Can Dance , which averaged 6.5 million viewers. However, Dance danced away with the strongest ratings among the 18-49 age group, leaving Dallas with about as many older viewers as Larry Hagman now has wrinkles.