Did u do this job yourself oh had shop do it?
Aligning the filter and removing the o-ring and installing a new one correctly is part of a good install too. Bad o ring install or none= problems.
Always use a gm/delco filter & gasket kit too.
Dexron 6 is the newest synthetic fluid, and transmissions work and perform better with it.
You serviced the transmission 3k miles ago, how many miles were on the old fluid?
It is a good idea to do the filter and fluid every 50k miles in the modern electronic transmissions, regardless of what they say. The friction modifiers do break down and heat is the transmissions enemy. I also add this to my transmission fluid which keeps it cooler and smoother, extend life of fluid too!
LUBEGARD Automatic Transmission Fluid Protectant