Hey, new guy here. I don't have a Ranger or B-Series, but I do have Ford's older B-Series counterpart. 1979 Ford Courier, 2.3L/5-spd. I have had a bad rear end shake since I bought the truck nearly three years ago, so I'm sure it existed well before then. It only happens around 60-70 mph, and there is also a kind of buzzing/humming sound whenever I'm coasting to a stop in neutral. I have:

• Replaced and balanced the tires several times
• Rotated the tires several times
• Replaced all four wheel bearings
• Replaced steering linkage
• Replaced front suspension
• Balanced driveshaft twice
• Replaced driveshaft center bearing
• Replaced all three U-joints
• Checked rear wheel lateral and radial runout
• Had the front end aligned three or four times
• Checked engine and trans. mounts

And yet the issue persists. Any opinions or help would be greatly appreciated as I am stumped and this problem is driving me bonkers!