Is my *istDS wearing out? Lenses? Brain?

[studiojmm]

So, I'm finding my camera when on autofocus and autoexpose mode just doesn't work as well as it used to . . .

I'm using a Pentax *istDS with a Tamron 18-300 most of the time. My first instinct is that it's the lens. I purchased this lens in 2006 for a long trip through China where weight was an issue and it served me really well as my only lens (there were points climbing holy mountains in July heat where I considered chucking my toiletries to get more weight off my back so I'm glad I wasn't carrying an extra lens). However, the camera hit a concrete church floor in 2009 lens down and I thought I might have done some real damage, but it performed ok for the rest of the trip. Since then though, I find it gets stuck finding the focus or stops focusing at an out-of-focus point, especially in low lighting.

My only other AF lens is a 28-70 Quandary that I got for some ridiculously discounted price at a going out of business sale for when I want the camera and lens combo to be super light and I don't need much zoom. After some fairly light use, it doesn't AF all that well either. I've been running on the assumption that this lens wasn't all that great to start with.

However, overall, I'm noticing also a heighten tendency of my *istDS to underexpose the images when in the auto settings and find myself lightening all lot more images than I think I used to. But I also have a couple bright sun shots that are ridiculously over exposed for the first time ever. (I've confirmed the exposure compensation settings are at 0.)

Thoughts on what is going on here? Is the camera, the lens, or maybe my brain? As the parent of a toddler, I haven't had been as focused on photography in the last couple of years and am more likely to be shooting in less-than-ideal lighting, but I still find myself dissatisfied by the exposure more than I feel I should be . . .

Thanks.

[idb]

Hi and welcome to dPs.

I would say "all of the above" are possibilities. My best advice is to borrow, beg or steal a new lens and try it out, even in a camera shop. The results will show you if it's your lenses at fault or your camera. Btw, I suggest NOT taking your toddler with you in order to rule out that part of the equation.
There is also this web site that will tell you if your camera's shutter is getting worn out:
Camera Shutter Life Database

Best of luck!
Ian