Vibration I Cannot Locate the Source of (please help)

Hello-

I have a 2011 Tacoma (V6 - 4WD - 6 speed manual - 157,XXX miles - not lifted - tires are Goodyear Wrangler Duratrac 265/75R16).

The Problem:
For the past ~500 miles I have been noticing a vibration that occurs at speed in my Tacoma. The vibration is loudest at 50 mph, it becomes less intense when I turn left (drivers perspective left) at speed, and is at its loudest when I turn right at speed. It makes little-to-no vibration both below 40 mph and above 65 mph. The best way to explain the vibration that I can come up with is that it sounds exactly like a bad wheel bearing (seemingly coming from the passenger side?).

Work Done so Far:
Up until this point I have been doing most troubleshooting and work myself. In the past week and a half, I have replaced both the driver and passenger side CV axles, wheel bearings, and lower ball joints. I also replaced the drivers side needle bearing (in the front differential) with the ECGS Bushing kit. I changed the gear oil in my front differential and transfer case (oil looked good in both coming out, used

$29 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 full synthetic). I normally change oil in these every ~50K miles anyway.

More Details on the Truck:
Laying under the truck, I don't feel any play whatsoever in the driveshaft joints- everything seems healthy from what I can tell. I have also been greasing all of the U-Joints with every oil change ever since I got this truck (at ~34,000 miles). The tires are new as of about a month ago, but I should note this vibration was occurring just before I got the new tires. I took it to a transmission shop last week and asked them to weigh in on what it may be. They put it on a lift, put it in 4WD, got it up to speed, and put a bar up to both the front wheel bearings to listen. The shop didn't detect anything suspect in the wheel bearings, though they did not deny that something is definitely wrong. This was before I did my passenger side wheel bearing also, and they suggested trying to replace that one, so I did... but that didn't fix the issue.

The Question:
At this point I'm out of ideas and I'm turning to this forum for assistance. I am thinking it may be time to hand the truck over to the transmission shop for analysis- but first, does anyone have any thoughts on what could be going on here?

Could it maybe be bad U-joints? But why would the vibration go away when turning left? Also thinking maybe the same thing about an unbalanced tire, wouldn't that be unaffected by turning? Lastly, could it be something in the transfer case / transmission / or rear end?

I'd gladly appreciate any insight,
Thank you!

 

I'm no mechanic, so take what I say with a grain of salt, but could the problem be within the front differential itself? something like a bad diff and/or pinion bearing. Because it looks like you have replaced almost everything else it could be.

 

The change when turning makes me think wheel bearing, but not sure why it would cause a vibration. I would expect more of a grinding/hum.
Spit balling here but have you checked the rear wheel bearings?

 

I have not looked into the rear wheel bearings, but I'm thinking I need to investigate.

Also, I am not sure if taking things apart inside the front differential is something I want to get involved with personally... unless it actually isn't that difficult of a job? Otherwise I'll be waiting until 4/4 to be seen by the transmission shop.