Front wheels locked up, in reverse

I have a 2010 tacoma, 136,000 miles, lifted. I have replaced almost every component on the front end. Ball joints, cv, tie rods and bearings are either new, or in good condition. When I put the truck in reverse, the front wheels lock up. Had the brakes checked out at a tire shop, they assured me all is well. The calipers are not locked up, the wheel turns freely. But as soon as you put it in reverse, there is a grinding noise, and the front end locks up.
Any suggestions?

 

can you move it forward?

 

Are you sure both front wheels lock up? There's not many (any?) things that can cause both front wheels to have the exact same problem.

 

Yes, with no issues.

 

I guess I'm not entirely sure if it's both wheels.

 

Although driving it anywhere could be dangerous, find some place with gravel or dirt. Back up and then get out and look at the skid marks and see which wheel locked up. I suspect a missing caliper bolt.

Again-----Driving this truck anywhere could be dangerous.

 

Sounds like a caliper bolt backed out. Look behind your wheels at the rim and see if you can spot any scrub marks on it