I'd consider a couple more bits of testing, having been down a similar road.
First, find a new target. That banana might not be the best target, given the shape, and the contrast between the blue and yellow might not be good enough - especially since the blue label has yellow text and graphics. I could see that throwing the AF system.
For my initial testing, I used a piece of brown cardboard with a flo-orange sticker from the gun range. Very high contrast against a very uniform background.
Secondly, do a Speedlight Assisted Focus test. Basically, run the same test as you have on the new target then toss on a SpeedLight, and use AF-S and have the infrared assist you in locking on.
If you get similar result with this final test, I'd say that you have a problem. Whether that problem is with lens, camera, or a combination is a tougher call.