Bottom line, it was easy and I'm glad I did it.
For a bit of background... I have a '21 SLT 2500 gas. I had previously installed the transmission dipstick/tube because... it should have a damn transmission dipstick! Since I tow more with this truck than my last one, I also wanted to make fluid changes easy, so I wanted a pan with a drain plug..
I went with the PML standard capacity pan. It not only provides a magnetic drain plug, but it also retains the fill-level port of the stock pan, making refills fairly fool-proof.
There's a ton of videos out there showing the clearance issues with the 6L80 pan and the exhaust cross over on half-tons and Yukon/Suburbans. Looks like a nightmare to fully remove the pan just to do a filter change on those. I can report on the '21 HDs there is plenty of room to remove the old pan and install the cast aluminum version.
I put the truck on ramps, and vacuumed out as much fluid as I could get with my extractor... about 4 qts. Unbolting the pan resulted in no additional fluid spilling out all over the place. There was still 1-2 qts in the bottom of the pan. At 45k miles, there was an expected amount of fine metal particles on the magnet, nothing out of the ordinary. Fluid was somewhat darkened but not burnt.
I cleaned and reused the gasket, bolted the new pan on, torqued it down. Easy access to all bolts with a 1/4" torque wrench and allen socket. The PML pan comes with new, longer allen head screws to accommodate the much thicker flange.
Poured 5 qts of Delco dex VI in via the transmission dipstick tube... which should have been there from the factory. Backed it off the ramps and drove around the block to get the temp up to ~110F. While idling I removed the check plug and poured in another half quart... no leakage. Added the rest of the 6th qt and saw it running out. When it slowed to a drip, put the check plug and called it done.
It's not the cheapest mod there is, but it's a high quality part, easy install, and easy future maintenance made it worth it for me.