07 ss/sc suddenly wont shift into reverse... Only 28000 miles and was working fine earlier today but now it just wont go into reverse

 

Does it go into reverse with the engine shut off? If it does it maybe a clutch problem, not releasing fully and so check the clutch hydralic system for leaks, try to bleed it. If the trans will not go into gear with the engine off it could be as simple as a shift cable adjustment problem, if the cables are ok it maybe internal trans problem. Hope that helps