2005 Toyota Tundra rear end differential?

I recently had my truck serviced at toyota and explained that I felt a vibration in steering column and felt a shaking quality when starting acceleration. It seems to be in the rear. Toyota said it was my rear differential and could cost several thousand dollars to repair w/tax. How do I evaluate this? With all that I read on symptoms of a differential problem it doesn't seem to apply. It also seems to loose some power when driving, then regains power. Help