This would be a decent alternative:
Night 4 - Green River UT, get an early start, drive through Hanksville and Torrey, making a quick trip through Capitol Reef, on to Tropic or Panguitch (or camp in Bryce) for night 5. Lodging at the park entrance is expen$ive.
See Bryce, go into Panguitch and take UT-143 to UT-148 through Cedar Breaks to UT-14 to Cedar City for night 6. Lodging in Springdale is expen$ive.
Head to Zion, park in Springdale, take the shuttle buses around the park, on to St. George for night 7 and Bishop or Bakersfield for night 8.
Buy the parks pass at the first park you come to - which will probably be Capitol Reef.