Beware: KitchenAid mixers just milking their name and reputation.
I've always loved my KitchenAid mixers, and considered them a workhorse in my kitchen. However, recently I began to get into bread/pizza dough making, and my 600 Professional Series unit burned out while kneading pizza dough (4 cups of flour) Since it was 2 1/2 years old and repair was estimated to be about 75% of the cost of a new one, I just ordered an exact replacement. Plus, being a huge Alton Brown fan, I know he had recent recommendations for KitchenAid mixers, so I didn't feel the need to research before buying another.
Since I could hear the previous unit struggling, with this unit, I cut my batch down to 3 cups of flour. It would still struggle at very low speeds and occasionally lock up, so I up'd it to a speed of "4". That enabled it to overcome the stalling problem, but the head of the unit did continue to get very warm (KitchenAid says this is normal - sometimes even too hot to touch).
Anyway, on my second 3 cup batch of dough (two days later), the unit stripped out, just like the previous unit. You could hear that the gears must have just completely disengaged and were flinging around loose within the unit (sounded like broken glass in a blender). Certainly this The first 3 questions KitchenAid asked me were:
1)"Were you making dough when the unit failed?" (Yes)
2)"How many cups of flour was the batch?" (3 Cups)
3)"What was the maximum speed you used?" (4)
She then said that the unit wouldn't be covered under warranty because it was considered "customer abuse" to use a speed over 2 for kneading dough and the Professional 600 6QT unit isn't rated for more than 2 cups of flour when making dough. After looking it up, the Owner's Manual does suggest a speed of 2 for kneading dough, but no mention of a cup-of-flour limit.
After some research on the net, it seems that while KitchenAid advertises that their mixers have metal gears (true), they don't mention that sometime after their purchase by Whirlpool, they switched some key parts, including the part that holds the gears together from metal to plastic. When the unit gets too warm, the plastic softens and the metal gears fly apart.
If you have an older unit, you're probably OK. I wish I hadn't "upgraded" my very reliable, but older (and smaller) unit to the 6QT Pro a few years ago. But apparently, KitchenAid made the choice to radically downgrade their units because they know that 95% of the market only uses their units for mixing batters, mashed potatoes, etc. and will never be affected by the drop in quality. I fell into this group for the past few years - never a problem until getting into breads.
I'll have no problem returning the unit to Amazon, so I'm not concerned about getting my money back, but just wanted to warn others out their who just by default assume that KitchenAid is the way to go for stand mixers. It used to be true, but these aren't your parents' mixers anymore (or even the ones you had 10 years ago).
Going to give a completely different type of mixer a shot (Electrolux Assistent) where the bowl rotates (same as my Mom used to have when I was growing up). Supposed to be fantastic for doughs, and decent enough for other mixing tasks. Can't speak to that fact yet since I've never used one, but I'm keeping my fingers crossed.