2005 silverado z71 transmission problems
 

Just bought this truck a month ago and I'm already having some transmission problems. First it started shifting hard into first now I'm hearing a whining noise when I drive. It shifts fine in every other gear. I don't think the truck was used to haul anything real big it has 105000 miles on it. I'm not really a mechanic by any means. Would appreciate any help I could get.

Whining noise? Is it all the time or just while it shifts? Usually whining can be traced to the rear end if it's drivetrain