Abs And Brake Light On

[fisher725]

I have a 2000 GMC Sierra 2500 4x4 and yesterday the ABS and Brake light came on when driving to town. The speedo started going crazy and eventually stopped working. The transmission does not want to shift properly now either. I did manage to get it somewhere to pull the codes. The codes that are present are C0281, C0236, C0237, and C0265. I am going to start by checking the ground wires per what I have read on here. It is sounding like the module but wanted some opinions on this problem. Any input is appreciated.

[asc08]

The speedo and shifting issues sound like it may be related to the vehicle speed sensor. This may also throw a code for the ABS.