You can drop the pan, however the 4T80 transmission is one of GM's BEST EVER. I highly doubt it needs doing.
If you do it yourself, here's a couple tips:
The "filters" under the bottom pan are no more than screens. They do NOT need to be replaced, just flush them out with carb clean or brake clean or hot water or whatever and dry them.
This is a "dry sump" transmission. The fluid in the bottom is barely 1/8th the total capacity. There is an ADDITIONAL drain plug inside, accessible once the lower pan is off. Once you remove the pan, there's a 7/16 (11mm) plug that must be removed to completely drain the trans.
It will take more than the average trans service to refill, somewhere around 8 quarts IIRC.
Like I said originally, these transmissions are almost bulletproof. The early ones had shift solenoid issues, but that was rectified in mid-00 I believe. I've had one of these bad boys apart, the parts inside are MASSIVE. Even the N* is no real challenge for the 4T80. If GM had been able to squeeze a 4T80 behind the 5.3 in the Impala SS/Grand Prix GXP/Buick Lacrosse super, they would have had a lot fewer issues. Unfortunately, the '80 is a huge trans and just won't fit...