Help me with T1i Focus problems

I love (with one exception) the used Rebel T1i with 18-55 that I got for my daughter from KEH last week. Great size, Hi rez screen, live view and movie, buffer, great color and WB, better hi ISO than my Nikons, other pluses too.

I do have one big problem with it though and that is focusing errors. Whenever I shoot a medium to low contrast scene, mostly foliage, dense treeline at the edge of a field etc, the camera indicates a AF lock, but when viewing on PC monitor, the focus appears to be on nothing in particular a few feet away from me. It is as if the camera could not achieve focus on my intended subject 50-100 yards away, so by default just focused at about one third of its range. I shoot consumer grade Nikons D70, D80, D3000 and never have this problem. I am having this problem mostly mid day, overcast but very bright. Its hard to believe that this otherwise great camera has this much problem focusing under these conditions. Do others users have this problem with this model or other canon models? Is my AF sensor dirty. I would rather have an indication of no focus than an AF confirmation that is grossly inaccurate. I am not new to AF cameras and understand the need for contrast, and AF sensors being larger than the AF box on the screen, etc. When I bought my first DSLR in 2004 I tested a Canon 10D and a Nikon D70. Loved the 10D but bought the D70 because of similar and random focus issues with the 10D.
Any thoughts? I would love to buy this camera but not with this problem.
Trying to work out posting examples.