Speedometer will drop to zero sometimes or peg out then ABS lights flash wtf????

Just started yesterday morning on way home from work. My ABS lights stay on because there is a bad relay in the computer but when driving down the road they are stating to shut off then come right back on. Then after a little bit off driving my speedo will start reading erratically then go back normal and ABS lights will shut off for a few seconds then come back on. And when the speedo acts up it will either drop to zero then shoot back to whatever speed I'm driving or it will hit 120 then drop back down. Also tried turning cruise on and when it does its little deal it will cancel cruise. Any ideas???? I'm leaning toward the speed sensor on the rear diff but just wanna make sure

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