Driveline pulsating?

I recently picked up a '06 Accesscab 4cyl, 4x4 and started noticing a pulsating between 45-55 mph in 5th gear. Everything else runs great, don't notice it in any other gear, even 4th at 50 mph, but if I'm in 5th gear anywhere betweeen those speeds I get a pulsating that I can feel in the steering wheel and hear a bit, not like an unbalanced tire though, like it's coming from the driveline. It goes away if I put it in neutral and I only tried once but it wouldn't do it in 4H. I've read about people's problems w/ vibration, but this is more of a rhythmic pulsing, not sure if it's the same thing. I'm def. taking it back to the dealer to look at but I wanted to see if anyone might have experienced this before.

 

im gonna go ahead and say its probably the center support bearing, cause some of them on the newer tacomas arent too smooth when the drive shaft is turning, and some have been having a problem with the whole drive shaft being the problem. the best way to remedy that,since the dealership likes to say its normal(i had an 06 myself.....vibrating isnt normal....i dont care what they sday)is to buy and install a tom woods drive shaft.......this has taken care of alot of peoples problems.

 

There is a TSB on the rear tranny mount.

I think its for vibration at a lower speed. Could still be an isolated problem.

http://www.tacomaworld.com/forum/2nd-gen-tacomas/7107-tsb-list-2005-2008-toyota-tacoma.html