Sounds like one or more of your brake calipers are binding/sticking. The problem could be that a caliper pin is binding and not letting the caliper go back to a nuetral position. (I had a left rear caliper pin sieze up and on occasion, the whole truck would shudder going down the road). The caiper pin looked like it was welded into the cailper. I broke/sheared off two T-55 torx bits and twisted a 3rd around where it looked like a drill bit before it broke loose (after applying heat to the pin). There was no lubrication left on the pin causing the caliper to bind against the disk.
If the caliper pins are ok, then you may have some foreign material blocking the brake fluid to return through the master cylinder or ABS system.
Also, if you have the disk brakes in the rear, check the status of the brake shoes that are used for the emergency brake system. If the mechanic just checked the condition of the pads and didn't remove the disks, there is no means to inspect the brake shoes of the E-brake.