I know this may sound stupid...but can't find the transmission filter. Was driving car and kept losing gears (automatic). Got it home, fluid seems fine. Could it just be a plugged filter?

Sure but the filter is inside the transmission. ussally the pan on the bottom of the transmission needs to be removed and and filter is connected to the transmission inside this cover on the lowest point. If your not a regular mechanic ( work on cars for a living, day in and out) you should hire this work done by someone who does.

The filter is located inside the transmission, you must drop the pan off the transmission to change the filter which by the way is not very likely to be the problem.

Transmission filters are usually internal and can be accessed by removing the transmission oil pan.