Can a T3i slowly start to lose focus (progressively get worse)?

I've had my T3i for about 3 years and maybe 25K clicks. I'm trying to test out a new 80-200 L Drainpipe on it and the focus is all over the place. I'm getting keepers maybe 2 out of 10.
The last telephoto I used before this was a 55-250 about 3 months ago and I'd at least get 8 or 9 out of 10 on the money.

I've been shooting equestrian for several years and never had this issue before using 55-250's, 55-250 STM's and 70-200 f4's ... all at max aperture and usually 1/1250 up to 1/2000.

I'm a little befuddled here. Anyone have any experience with this?? Could it possibly be the Drainpipe??

Focus, when it misses is usually 10 to 20ft behind the subject but often in front as well. I was thinking MFA, which I can't adjust on the Rebel, but that should be consistently one way or another. The camera has always been dead on in the past, and nothing physical (damage wise) has occurred.

Any thoughts would be appreciated!

If the camera has always worked, I would suspect that the lens is at fault. It probably does need some sort of adjustment. Either way you'll have to send both to Canon for calibration.

I suspect the 80-200 L Drainpipe..

rrblint wrote in post #17639886
If the camera has always worked, I would suspect that the lens is at fault. It probably does need some sort of adjustment. Either way you'll have to send both to Canon for calibration.

Be careful here. Calibrating the camera to the 80-200L could effect his other lenses.

My understanding is Canon will not even touch the 80-200 anymore. It was a flier buying it, but wondering with the old AF motors maybe tracking horses at a full gallop maybe a but much for it? Shooting less movement it takes beautiful shots, but I need that lightning fast AF.

Without the ability to do this type of shooting, I have to switch back to a 70-200 f4. I just though it may be worth a try on the Drainpipe. Shame, it's a flawless copy with great glass ... maybe just not but out for this application.
The Rebel was spot on the other month shooting a golf outing with the 55-250 kit lens, so I'm doubting blame can go to that.

My 1D is at Canon now, so using that to test isn't an option and I need to shoot this weekend.