After owning a used one of these lenses, I decided to buy the new version to see if anything had changed. Other than a slight update of the look, it performed the same. I was hoping the AF motor would work faster.
Recently, I thought I was going crazy because I couldn't seem to take a sharp picture to save my life. I was also getting a LOT of ERR 99s. I tried cleaning contacts and removing/replacing the battery, and nothing seemed to help. So I sent the lens in to Tamron. I got a repair letter back from them and this is what it said. (Mind you, I've only owned this one for about 7-8 months.
FOCUS IS OFF
ZOOM IS LOOSE/TIGHTEN
ZOOM IS ROUGH
LOCKS UP CAMERA/SHOWS BATTERY MARK
APERATURE ASSEMBLY NEEDS ADJUSTMENT/REPLACEMENT
CALIBRATE TO FACTORY SPECS
Seems to me that is a long list for such short ownership!
I also bought a used one of these recently off of ebay because it was a package deal I couldn't pass up. This one is from 1998 and has had several repairs done to it, including replacement of aperature. The previous owner included all of the paperwork.
However this one seems to work just great. So go figure. Still slow on AF, though, which makes me want to upgrade to canon lenses to get the speed. After using my 17-40 USM L and 28-135 IS USM, it makes me very impatient waiting.