Automatic Transmission question

Just changed the fluid and filter, it ran low and the fluid was a bit burnt. Would only run in first gear before I changed it and was slow to engage. After the new filter and proper fluid level, it shifts promptly and strong up through 2nd gear... where it drops out of gear and revs. While I know it may be bad, does anyone know of things I can check (vacuum, control connections) before I worry about replacing or rebuilding the transmission.

year and engine? might wanna try a fluid flush...
my friend's mx6 has the exact same problem on his 94 4 banger mx6.
I'm gonna work on it when he gets some money.
but I'll look it to it...i go to a tech school.

It's a '93, 4 cylinder. According to my Haynes manual the capacity is 6 quarts and I had to replace 5 to bring it full after draining about 1.5 quarts. I tried a few more things last night and it does appear to go into 3rd as long as I don't press the gas. When I do, it slips right out of gear again. The consensus I seem to be getting from people is the bands for 3rd gear are gone.