I've replaced my speed sensor before and it's like replacing an o2 sensor...usually isn't the problem. Not a chevy, but I own a company and one of our ford vans at heavy throttle and WOT would do the exact same thing and ready for this...new alternator fixed it. Doesn't mean that's your problem, any other symptoms to speak of? dead battery recently? sputtering? does the motor sputter in the slightest when this happens? No codes? If a speed sensor starts to take a dump on you you should get some related code...like incorrect gear ratio and ect. It is odd that the abs light is talking to you at the same time...pay the hour fee to have a tech hook up and reproduce the problem. If that abs light is on, they'll read the code.

 

Ok Ill go and romp on it and then get them to read the code. I am throwing a code but that is a knocking code because i am tuned in such a way that my timing is retarded up to 2500rpm to get the single tire fire off the line. Alternator huh? It actually sounds like it is somewhat plausible. I mean if the motor is spinning at such a high rpm then isnt the alternater spining even faster right and there is a possibility for there to be some kind of glitch or something. brand new battery about a year ago but the problem was present before then. But like I said at high rpm the spedo flips and flops and doesnt know what the hell to do and the parking brake light flashes for a split second and then the abs light comes on. Is there more than just one code an abs light can throw? But you are right, the alternater does not explain the abs light.