I know EXACTLY what you mean, Mary (about both the tea and the diet A&W).
I can't take full credit for the science behind the tea thing. It's mostly stolen from Cook's Illustrated, but it made a huge difference for me. The keys are to NOT have the tea in contact with the water for very long and to not have the water too hot.
Here's what I do:
Start a quart or so of water in your teakettle.
Get out 10 Lipton teabags. Tie the strings together (I do two batches of five and then tie those two batches together). Strip off the little paper tags on the end of the strings.
Throw the teabags into the bottom of a ~ half-gallon glass pitcher.
Listen to your teakettle. Don't let it boil. Just BEFORE it's going to boil, pull it off the heat.
Dump the hot water onto the tabags.
Set a timer for three minutes and start it.
When the timer beeps, immediately pull the teabags from the pitcher.
If you like sweet tea, this is a good time to add sugar. Fill the rest of the pitcher up with nice, cold filtered water or ice.
Relax on your verandah.