Used Spark Plug Diagnostic...

Just want to confirm what I've read on here:

See pics of driver side rear plug below. By far the dirtiest plug, and the only wet one. Should I be concerned about this, or just keep truckin... @ 135,000 plus miles 2005 pre runner TRD Double Cab, 1GR-FE. Also Changed oil and air filter to AFE Pro Dry. Removed Sparks were NGK R's, both sides. The reason for Tune up is b/c I've been getting some different engine sounding noise once i get over 30mph, almost like the engine is having to work harder. More obvious releasing gas pedal, almost feel like engine is trying to slow down on the down shift. No check lights and temps look good. Oil was a little dirty, ran about 8,000 on gtx syn blend.

Any thoughts on this? Really wanted this to be the DD for at least 200,000 miles.

Thanks for the help.

 

Thanks, Chris. A few more pics for reference. So I thought the new sparks would alleviate the engine noise issue... but that area seems to be ok... maybe something to do with timing, shifting/tranny maybe... at a lost.

 

Just badly worn out.

 

ill say they are too. go with densos they last longer

 

Top speed 30-40, driving to interstate:
https://drive.google.com/file/d/0B7nYTHDfSSsSUWkwa3dqSGdOaEpDTVk0bkRaNXo5d3ZIdmxF/view?usp=sharing


Top Speed 70-85, vibration at 60. Noise I'm talking about is around 50-80, throaty engine noise upon acceleration and coasting. Wasn't always there...
https://drive.google.com/file/d/0B7nYTHDfSSsSNWVOeXpyV085eVBYbmtQNGZDbGo4akNsRWNZ/view?usp=sharing

**Update 6/1/15**
After thinking about it, I'm pretty sure i have bad Driver Side rear axle bearing...

I remember taking it to midas a year ago, to repair rear " break squeak", which was actually rear axle oil that had gotten on my brake shoes. The guy cleaned it up and it didn't squeak=out of site out of mind. Well now it looks like I'm probably gonna be replacing seals/bearings. I've also heard, if your doing one side, do the other.

So moving forward what can i expect in price, associated parts, problems, ect.

I guess I'm going to start with a few quotes and see if its worth DIY. Let me know anyone else's experience... Taking to firestone for free alignment balance. I'll have them check bearings, seals, ect. Should I have them check anything else?? Don't trust them to actually do this work however.

**Update 6/6/15**

After making my 7am appt at firestone for free rotation (nothing's free) I waited 1.5 hrs to rotate 4 tires and tell me I had a bad wheel bearing in the passanger side. See attached quote. Therefore I bought the completed assembly from here http://marionbumper2bumper.com/store/index.html and also a few torque wrenches from Amazon for under $500. Will plan to tackle this bearing ASAP. Does anyone have any experience with replacing one of these in the garage with basic tools? What can I expect in time? 4Hrs? I'm going to start soaking the bolts around the wheel hub in wd-40. Any other tips/tricks would be helpful!

Thanks!