Alright I have a HUGE NEWBIE question, I was wondering what weight of fluid is the thickest....sorry for such a pathetic question but I dont have a clue.

 

doesn't matter... unless you have a Ford, Mopar, or HIGHLY modified or custom gearbox that the builder says calls for something special, you're going to use either DexronII-Mercon or Dexron III. that is, of course, unless you're talking about a manual tranny. they typically call for 80W90, but that too has a manufacturer specification for a reason. automatic transmission oil is just thin hydraulic fluid; different grades are thicker than others, but DO NOT run other than specified fluid in your transmission unless you just happen to have several hundred dollars to blow.