So recently my 04 Expedition (4R70W) has started having a problem. The 1-2 shift is delayed and doesn't want to shift till about 2500-3000 RPMs. All other up/downshifts work fine and feel like normal. I pulled the pan (discovered no magnet...) then pulled the valve body to remove the 1-2 accumulator. there was no broken springs or other issues I could see.

Anyone have any idea where to go next?

I am going to look at the valve body now, but I'm having a hard time finding hydraulic diagrams for 1st, 2nd, and the 1-2 shift. Also I've read other people have had TPS sensor issues, but it's only affecting the 1-2 shift and I should notice it on other gears. Sometimes after quick repetition from 1-2 to 2-1 to 1-2 it doesn't delay as long and almost seems normal.

What could it be?

 

Well no responses, but I thought I'd follow it up.

Everything in the valve body seemed fine. I did pull all valves out to clean it. The separator plate was starting to crack where the 2/3 accumulator hits it (known problem). I replaced it with the thicker aftermarket plate that also comes with a cup for the metal thing in the 2-3 accumulator. I installed new gaskets and it took 11 qts to fill it. shifts better than ever, but I don't know what fixed the shifting issue. The biggest thing I was worried about was a broken spring and it wasn't that.