Klaus gave you a great tip for resolving your ABS codes. I didn't know about that one. All those ABS codes will probably go away together. I posted a response, and Klaus concurred, that one code is the O2 sensor. These seem like reasonable codes to come up, so I wouldn't jump to the conclusion you have a bad computer.

Your main problem seems to be the transmission, so you might just ignore the ABS and O2 codes for now. The A1 code comes along with the flashing arrow and "limp home" mode (3rd gear), and in turn will trigger the Check Engine. But right now, the other codes will trigger Check Engine also.

The bottom line is, only the A1 code is related to your transmission problem and the flashing arrow. Klaus gave you a tip to check your transmission fluid. Some people have success at improving a quirky transmission by changing the fluid.