The AW experiment was a fiasco. The show had been #1 or #2 in the ratings for several years (due mostly to the writing and its theatrical style) but in 1977-78 the new, shiny thing was General Hospital, with its emphasis on youth and energetic style. AW was about to experience a ratings downturn, though they of course did not know it at the time. When NBC decided to expand it to 90 minutes, GH (and to a lesser extent, All My Children) were taking away viewers. The production team and writers had been working on AW for years and were likely overworked--so now they were saddled with producing another 2 1/2 hours of the show per week!
The big stars of the show could not appear every day, nor could they memorize 90 minutes of dialogue on a regular basis. The Mac/Rachel/Iris triangle that had carried the show for so many years had to be back-burnered because they could not get the actors to 'overlap' in their workdays. They could schedule one or perhaps two of them to appear, but rarely could all three appear at the same time. They had to ration out the appearances of those three, and the balance of the time had to be filled up with new character additions. Viewers felt cheated if none of the favorites were appearing that day, and of course no one likes to see a bunch of newbies "taking over their show". Both the Executive Producer (who was responsible for the theatrical style and "look") and the Head Writer departed due mostly to burnout. The second-stringers who took the reins were not up to the challenge, so the stories they came up with were pretty bad. The decision was made to create a spin-off series starring Beverlee McKinsey (who played Iris) and to reduce AW back to 60 minutes. This allowed AW to write out a lot of the characters who were not working out, and focus more on Mac/Rachel once Iris was out of their hair. Texas only lasted two years, and AW fell into a cycle of hiring and firing writers and producers that caused their ratings to go down and never recover. The 90-minute experiment seriously wounded AW, and the obvious problems of trying to put on a 90-minute soap warned everyone else off of trying it.