i have a 99 f-150 4x4 i have resurfaced the rotors and changed the pads but the rear drivers side brake makes a noise like a semi truck stopping when i brake at low speed could it be i might need a new caliper

 

go for a good drive and check if that side is heating up more than the otherside maybe caliper is sticking and check your sliders to make sure they arent siezed

 

Also check for rear diff fluid contaminating the new pads and freshly turned rotors. It's easy for an unexperienced eye to miss an axle leak. Again, un unexperienced person may also install a brake pad backwards(don't be embarrassed, it's been done by veteran techs... not me!!!! I swear!!!). Make sure caliper bolts are tight. The rear pads..... are designed to go on one way. Notice the grooves or hooks at the top and bottom of each backing plate on the pads. The left side should be hooked to the axle from the bottom, the right side should be hooked from the bottom as well, each side resisting the turning force of the wheel. Imagine having a caliper and brake pads clamp down on a spinning rotor with no real anchor other than a 6/1.25mm thread bolt holding it down. The pads are made for the left and right side.

You may also have a bad ABS sensor in the pumpkin causing the ABS system to kick on (in rare cases). I'd think the rear ABS sensor wouldn't cause a noise in the rear, but rather a fast pulsation in the pedal and a noise from the left front area(ABS motor) and definately a coherance fault code in the ABS module. Check the simple stuff first as I mentioned in the first paragraph. I think you'll find a relatively simple mistake made in the brake work.