I've notice lately while the carbed engine idles in park too long, the darn fuel needle slowly tracks up to F back to midrange, then slowly down to about an 1/8th tank. Whats up with this? Is there something electronic in my sending unit acting up.

 

Someone had a similar post on this subject not long ago. Everyone said they have the same problem so it's nothing new to third gens. The fuel gauge is very inaccurate and it will move around a lot. Sometimes it will go up after setting overnight, sometimes it will drop fast in the last half. So just use it as an estimate of what's really happening.
Save your money and don't replace anything, they all act the same way.
Good luck,
Ozman