I'm stuck in four wheel drive (auto 4wd)

i have a 2001 LT suburban with auto-trac and i pushed the auto 4wd button and immediately my service 4wd light came on and i was unable to go back to 2 hi (same thing with 4hi/lo). The auto 4wd light is on so i don't think that it's the button, maybe the solenoid or actuator? Also, i recently had the transmission pulled and the rear main seal and oil pan gasket changed and they cleaned the undercarriage with engine degreaser.  -thanks in advance, Brad