I have a 2001 slt v6 automatic. Just changed the fluid and filter. Ran great for a week or two now feels like it takes off from a dead stop in second gear. While sitting at a stop with trans in Drive you can feel it jump down into 1st gear and then back out. When you start off if you'll pump the gas pedel it will jump into 1st gear. Sometimes when your going about 30 or so and you stomp it, it will jump down into low gear and other times it want. It does all this cold or hot. Any help on what to check or change would be great. Thanks Oh yea works great if you put it in first gear with the shifter.

 

From the FSM:

MOVES IN 2ND OR 3RD GEAR, ABRUPTLY DOWNSHIFTS TO LOW

Valve Body Malfunction - Remove, clean and inspect. Look for stuck 1-2 valve or governor plug.

Governor Valve Sticking. Remove, clean and inspect. Replace faulty parts.

 

I'm thinking low hydraulic pressure, myself.