I just changed the transmission filter amd fluid on
my automatic 2004 4wd trailblazer. Now it runs
fine but it wont go into 3rd. It goes into first fine
amd goes into second fine but it just womt shift
into 3rd. It sounds like its trying to but it juat wont
make it. And ideas?
Well, I've seen this happen a few times, when you change the fluid in an older transmission. Sometimes little bits of grit or burnt fluid will get in the valves that control when the car shifts and get stuck. Sometimes you can flush it out, but a lot of the time it will just make it worse. I'd take it to a mechanic and see what they can do about it. It may need a rebuild. Although I recommend just getting a used transmission. Rebuilds are pretty pricey and they aren't done right almost half the time unless your mechanic knows what he is doing.
Recheck the fluid level hot and running, if it’s full then pull out 1 quart of fluid and add 1 can of TransX to the transmission and drive it around for about 20 minutes and then let it set a day or two, and then retry, if it shifts fine you dodged a bullet, if it doesn’t then it time for some transmission work. If it did work then Service it again in 5000 miles. Now if it was low on fluid that could cause your symptom