Lately I noticed that I get a mild surge or slip in the tranny especially going up a grade and between 4th and overdrive. Its NOT shaking or violent by any means and if I floor it it goes away. I've read in the tranny forum that it could be a COP or plug but just had plugs replaced last fall and I've only put 8K since then. COPS have never been replaced though. It does not throw a code either.
I'm original owner with almost 150K miles, transmission fluid changed every 60K. Any ideas? Thanks

 

Unfortunately could be many things. I was having a similar issue and mine was Cam Phasers. given your mileage that could be the issue. The other could be a bad over drive band/overdrive pin with broken C-clip. I would personally check that Cam Phasers are working properly.

 

I'd lean more toward cops.