Mystery transmission (?) quirk

[Snowcreature]

Hey all, just discovered T4R and hoping somebody more mechanical than me can give a few pointers.

Driving a '06 V6 4WD 4Runner with 70k miles, for the last 10k miles or so it's developed this thing where if the vehicle is cold (say, first 10-15min of operation) it feels like either the transmission might be slipping slightly or the engine is stumbling.

Here's when it happens:
1. Stopped but in drive, foot on brake. Every now and then feel a little lurch like it either started to shift into gear or the engine stumbled. Hard to tell.
2. Just getting on the gas, a little stumbling feeling when just starting to move.
3. At slow highway speeds, 45-55 mph, first off the gas and then coming gently on there's a significant clunk and jerk, like maybe the transmission was slow to shift and then got dropped into gear.

This ONLY happens if I've recently been doing a fair amount of highway driving (say in the last few days).

This almost never happens if there's been no highway driving recently.

Thoughts?

I'm guessing it's the transmission, but sure enough the 4Runner will never do it when I stop by the dealer for a mechanic to do a test drive...

 

[004Gunner]

Problem number 1 sounds a lot like the infamous driveshaft clunk. Greasing the driveshaft may get rid of it. See if this matches your symptoms.

 

[Snowcreature]

Thanks!

I'm dropping it at the Toyota dealer tomorrow, will have them do that. Plus will see whether they have any thoughts on the transmission. I imagine they're not transmission experts but maybe have seen something like this before.