1999 Ford Ranger Jerking in the rear of truck

INSPECTION

Visually examine front and rear tire and wheel assemblies for damage such as uneven wear, tread washouts, or side-wall damage. Make sure tires are of same size, type and same manufacturer (where possible). Any tire or wheel that is damaged should be replaced. Wheels and tires must be cleared of any foreign matter and tire pressures adjusted to correct specifications.
If tires exhibit uneven wear or feathering, cause must be corrected. Check steering and suspension components for damage or wear and check and adjust steering alignment (if necessary). Check hydraulic hoses and tubes for leaks, cracks, chaffing and distortions. Check fasteners that hold these components in place should also be checked.
NOTE:DO NOT pry under or otherwise disturb dust boot.

Check drum brakes for loose or worn parts. Check rear wheel cylinder for leakage around dust boot. Check for proper component installation, leakage, caliper slide lubrication and excessive wear along caliper supports. Check instrument cluster brake warning light.
Check that link from brake load sensor proportioning valve to frame is properly connected. Brake load sensor proportioning valve is calibrated for particular vehicle it is installed on. If modifications are made to rear suspension system, brake load sensor proportioning valve will not work properly and must be deactivated.