This is my problem I decided to change the transmission fluid and filter on my 2004 gmc sierra 4.3. So when I finished changing the oil i started the truck and took it for a cruise only to find out that now my truck does not want to shift gears it starts off real sluggish and then around 30-40 mph it seems ok do anyone have any idea what has happened and can give any info on fixing it. my check engine light went on and took it to autozone and the man said it pulled out the code for a shift solenoid, but told me this happens to the truck on a first change and to go home and let it run but i did and no dice. So if anyone can help me out i would really appreciate it.

 

drop the pan again.......you might have unplugged a solinoid when you pulled the filter off. My money is on that.