Sounds like the dump valves are not opening to allow brake fluid to release the brakes. Controlled by the ABS module, try disconnecting the ABS module and test the system w/o it being connected. The vehicle should still have normal brake functions, start off just forward and back to be sure that the brakes are working to stop you. Gradually increase speed and test brakes. If all seems to operate normal it seems that the brake module and or ABS pump are to blame. Hope this helps.