Had brake lines replaced to ABS unit. Now, the brakes on all four wheel lock up on 2004 Chevrolet Suburban 1500

error for stability control comes up. Mechanic has bled lines several times but same thing happens once you press brake pedal.
Any ideas for fixing problem?

Have the ABS autobleed function done with someone who has a Tech2 scan tool.
It turns out that hydroboost unit had a leak and because rear seal in master was no good, power steering fluid was being pumped into master cylinder. The rubber in master swelled up and lines to calipers open under pressure but collaping and not releasing.
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