So I've been fighting this problem since I bought the truck. It was like that when I bought it. Also the fluid was overfull before I drained it. Under any load conditions it'll slip shifting from 2-3. Most of the time it feels like 1-2 but it shifts from 1-2 before the speedo starts moving usually if you pay attention you'll feel it. The truck will go 1-2-3 before 15mph and lug up to speed in 3rd. I was given a new filter, gasket and fluid (correct fluid) when I bought it. I dropped the pan yesterday to find metal flakes in the pan. The only way to describe it was like a blowout near the hole in the valve body that the filter covers. It looks like something metal was sent down that tube and blew through the filter and hit the pan and kind of did a "splat" kind of effect that was about 3" in diameter. I know older autos the shavings are normal. It's uncommon not to have any. In newer cars the amount of metal would more than justify a replace. The filter was dirty but no metal. Magnet was full too. By the gaskets on the pan I know it's only been changed 2x in the truck's 200k miles. After changing it all the truck doesnt lug so bad but the quick 1-2-3 and slip from 2-3 is still there.
I read through the ESM diagnosis page. It only lists eratic shifting. And under that section pretty much everything is a culprit.
I'm wondering if there's any way around a rebuild/ replace. If I have to replace I'll swap in the 2.6 driveline from my first gen donor truck and convert it to 5-speed. Or will that trans bolt to the 2.4L?