Dealership can't figure out what the heck is wrong with my Taco.

Hah. Interesting. My 2015 does a similar thing. Started at around 5k miles, now at 12k. Basically all gear changes at low throttle result in a slightly clunky shift with a subtle shudder. Not enough to bother me too much but it's not consistent. It sometimes shifts very smoothly, especially right after cold starts. Put it in "4" and it's a lot smoother. Could the calibration be that different between"4" and "D"? Different line pressure perhaps? I asked at the dealer but because it's subtle they are quick to conclude it's "normal".

 

We had a 2007 FJ Cruiser that had the same problem. The only solution the dealership had was replace the tranny (6K but we were under warranty).

We traded the FJ within a month of the new tranny being installed.

 

Not that I feel it's related or anything, but the v6 engines aren't supposed to run iridium plugs. Figured I'd mention it.

 

If the OP's truck is a 4.0 and the plugs are original the OP is probably over due.

 

The dealer may have swapped the transmission but I'm wondering if they swapped the torque converter.

 

Yes. Twice.

 

Do you know if they reused any sensors?

 

I have no idea.

 

OP mentioned that he switched the plugs for iridiums. The plugs aren't old/due for change, but they are the "wrong" ones.

 

I changed the plugs and cleaned the throttle body. The plugs were toast, with gaps as wide as .0060 and burnt off electrodes. The issue has definitely reduced in frequency and severity, yet still persists. This leads me to believe it has to be an ignition fault of some variety. I have ordered a Bluetooth OBD2 scanner, and plan to use the Torque app to hopefully identify the source of the fault. I suspect a bad coil pack.

 

This sounds familiar to what I've been dealing with...

 

I had very similar issues. Spark plugs fixed it. NGK-R's..

 

Spark plugs did not fix the issue.

This passed weekend my tranny cooler ruptured, contaminating the coolant with tranny fluid and vice versa. Google: Dreaded Pink Milkshake. After a new radiator and a very expensive engine and transmission flush, the taco is up and running again. Poorly.

My theory and concern is this: the poor shifts may be caused by an elevated fluid pressure within the transmission (from any cause). This elevated fluid pressure also caused the tranny cooler to fail, and may again.

Thoughts?

 

Okay now I hate to be the one to tell you this but you have officially lost your friction discs in the transmission. The glue holding the friction material will begin delaminating after being exposed to coolant. The transmission my need rebuild soon to correct. Personally if I were you in would take the truck to a reputatable transmission shop and have it gone through.
The SLU valve controls line pressure if I remember correctly. Line pressure would have to go absolutely wild to burst the cooler tube in the radiator.
I'd bet it was plugged with debris causing the burst. Bad fuel injectors will cause an engine to run rough. Smell your oil for gasoline.

 

Because everything is better with pics:

 

Man that's bad.
I'd make the dealer pay but of course it's never their fault.

 

With all these problems, you would've thought the dealer would've given you a new truck

 

Low on ATF Fluid,Drain at Pan Drain Plug, Refill cold with 3.2 Quarts ATF WS and Replug, Operate in all gears shift back and forth, and drive for a few miles and 30 minutes or more,should be good after that,and recheck for leaks ! DONE!

 

If the truck is by some miracle still under the original warranty it would likely qualify under Lemon Law. It would have back in '10 more than likely.

If not I would probably sell it for salvage and walk away from it.

 

Sad. Terrible things have happened to you. Hope all will eventually work out. Sorry bro.