It would be a pretty strange coincidence for the tach and ABS problem to be caused by seperate issues, but stranger things have happened.
Have you cleaned your wheels where the ABS wheel speed sensor rests? Also the rear diff.
See my old thread too:
http://www.peachparts.com/shopforum/showthread.php?t=283865
I would wait till your relay gets installed before you worry too much as that is usually the culprit for this problem. It should also be affecting your AC compressor too....is it still engaging?