Yes the dipstick is just a tool, you have to reinstall the locking cap when your done. I just safety wire the lock so it doesn't come off when I'm done and viola, fresh fluid.
Your 99 should have a drain plug in the convertor, and your 2000 "might" as well. The elimination of the drains was started in 2000, so if you have an early 00 than you just might be one of the lucky ones and have a drain.
It only takes a second to look under there and find out.
Also I'm doing some research in ALLDATA trying to figure out where tranny temp. sensor is and what pin it is associated to. It might be possible to get a reading of the fluid temp using a stardard VOM meter for all of those out there who are adamant about the temp. being 80'C. I'll let everyone know if I can find it.