Very weird LGT 5EAT highway issue yesterday?

I have a bone stock '08 LGT 5EAT with 55k miles on it, I've owned it since new.
I was driving on the interstate through the Adirondack mountains at about 70 MPH yesterday as I've often done before, and all of a sudden as I'm climbing a hill the car starts bucking with the revs jumping up and down as if the lock-up on the converter is kicking in and out repeatedly, or as if it's stuck hunting between gears?
It just kept doing it up the hill, really caught me by surprise, I wasn't sure it was going to make it and it seemed to be loosing power? It has never done anything remotely like this before?
I did notice that although the car was in drive at the time, it was in S# mode, could that have something to do with it?
It was fine after for the rest of the trip (took it out of #S), No CEL, but from what I understand there could still be codes?
Appreciate any help.

All the best,

Paul

Bueller, Bueller, Bueller, anyone?




Paul

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Did you pull any codes?

I've seen a little bucking at the right speed, but nothing that had the revs bouncing.

If you take it out of full auto and put it in a gear what happens?

Originally Posted by rob-2

Did you pull any codes?

I've seen a little bucking at the right speed, but nothing that had the revs bouncing.

If you take it out of full auto and put it in a gear what happens?

Only did it that one time, had it checked and no codes at all.
That happened about two weeks ago now, the car is running absolutely fine and shifting perfectly.
I have to do another trip of a couple of hundred miles this week, we'll see what happens..,



Paul

How old is the fluid? Is there fluid?