lens problem question

Noob question. Lens is a Tamron 70-300 on an XT. Have had it almost a year and have done a ton of shots thru it no problems. Was watching some spring training games this past weekend, worked great on Sunday, come Monday, went to use it and whenever I have it zoomed in from about 250 on up it'll set a error 99 code on the camera when I try taking the photo and then way overexpose like its hanging the mirror up. Usually have to remove the lens and put it back on to get it reset. Tried in manual and AF as well as M setting on the camera (usually shoot in AV) with no changes. Camera works fine with the other lenses I had with me (Sigma 17-35 2.8-4 and a Sigma 24-70 2.8). Tried cleaning the contacts with no change. Likely sending to Tamron for RR (assuming warranty is still legit) but thought I'd ask around and see if anyone has had similar experience. Bad timing as I was going to move the lens with the camera as a package deal as I'm trying to upgrade to a 30d/40d and some slightly better glass, hate to have to buy a lens just to include.

On another note anyone have experience with Tamron on warranty work?

Thanks in advance.

Had a similar problem with a Tokina lens. It would work fine wide open but would often cause an error when stopped down. Turned out the aperture diaphragm was sticking. I was able to visually verify this by stopping down to f22 while looking into the front of the lens to see if the aperture was completely closing down as I pressed the DOF preview button.