Told drive shaft needs replacing???

Hi, I have a 98 tacoma,4wd,stick shift, bigger 6cyl.engine.93,000 miles.Noticed "clink" when shifting,mechanic suggested just to replace u-joint. Then he decided whole driveshaft ought be replaced due to wear. He installed a Toyota rebuilt drive shaft[he claims]. After that,there was still a clink,although fainter,,but a vibration began at 35mph.He next replaced driveshaft with another one sent him by Toyota,and vibration is less severe,but still there and now kicks in at 45mph. Why would a driveshaft need replacing and what could wear on it enought to need replacing? I am beginning to doubt this guys ability. Thanks Larry

could be the rear end more than anything. if you're spending that much money from that guy, you should just take it to a dealer and have them look at it.