So we've established that you have experienced the same, or at least very similar, issue with two bodies and two different lenses.

Is the K5 up to date with firmware?

I'm assuming you mean ISO priority (Sv - Sensitivity) mode. This is probably the least used and least useful mode to use with your camera, and if there were a glitch in the cameras exposure control system using this mode, it is not likely that many here will have had the problem.

You never had this mode on your film cameras, why use it now instead of the more useful and more widely used aperture priority (Av) mode?

John is not employed by Pentax, neither is this a Pentax sponsored forum. John is a forum moderator, here to keep order, and has been using the Pentax K mount for much longer than you have it seems.

If you maintain this attitude towards knowledgeable people who are trying to help you, that help will rapidly diminish.

That said, I'll try to help you. Just be respectful in your answer please.

Can you say whether or not the images that you have found to be over exposed on two bodies, were taken with the same lens? If they were, I'd start to suspect the lens, not the camera. As John points out, it may well be a lens to body electrical continuity issue. Take his advice and clean the contacts. If that doesn't remedy the situation, closely inspect the contacts on the lens for any physical damage, however minute.

Why?

The grip has the same threaded tripod mount that the camera does, which should not prevent the use of a tripod at all.

Thanks Ken & Oggy for the info about Eclipse 2. I didn't check the current recommendations before posting.

As a K20D owner, I have found no need of a wet cleaning system . . . yet.

I think I've only ever had to resort to a wet clean once, on a used *istD I bought several years ago.

I don't even use a blower nowadays, just the Arctic Butterfly. I found that the blower always seemed to shift the dust from the sensor to a much more inaccessible place behind the focussing screen.

My advice for bags of this size range is to buy a bag that is bigger than you think you need.

I can personally recommend the Fastpack 350, it's my most used, go everywhere bag.

Your camera model will influence your decision. Some of the older Pentax bodies could use Eclipse fluid. Newer ones require Eclipse 2 because of the coatings on the low-pass filter (the bit you actually clean).

I've never had any muck on mine that couldn't be shifted by the Arctic Butterfly so I can't recommend any particular wet solution.

If you use pre A series or soft lenses, the on board flash discharges 100% as it cannot be controlled/regulated. It's also possible (needs testing) that you won't get the pre-flash either.

If you need to prevent the pre-flash from firing, fit an older Pentax flash to your hot shoe. There are plenty of old flash models to choose from.

From the subject line, I had assumed that the OP already had the K5. I didn't read the whole post

Sell the K10D, the other two have far superior low light/high ISO capabilities. A K7 would provide very little improvement as a K10D replacement except for its similarity to the K5.

Looking at your sig., I'd also sell the DA 18-55, DA 17-70, and the Sigma 70-300mm. I'd replace the low FL lenses with a DA*16-50, and maybe even replace the DAL50-300mm with a DA*60-250.

On balance, I'd start replacing your lenses before the bodies.

I think the soft focus suits the subject very well.