I have been seeing more and more people with P3S issues.  So I thought it would be good to try and get everyone to post the specifics in one thread, so that it could maybe assist DJI in troubleshooting.  Because it seems clear that there IS a problem.  Most common issues I have seen are RC range,  Video signal range or drop out.  It would probably be helpful to mention what kind of device you are running the DJI-Go app on as well.
For me:

Consistent RC range trouble.  Drone goes RTH randomly due to loss of signal.  Any altitude,  any distance.

Intermittant loss of video signal.

I am using a Galaxy S5 running Android 5.0.

It is worth mentioning,  I solved my RC range problems by buying a 5.8 ghz inline amplifier.  50 dollars.  Requires a mod to the RC.  Replace stock 5.8 ghz antenna with a new pigtail and bulkhead connector that mounts where the old antenna was.  Connect the amp to the new connector,  screw the new antenna onto the output side of the amp.  The amplifier runs on from 9 to 16vdc.  So,  you need a small battery.  I use a 12 volt gel cel motorcycle battery.  Very light weight and plenty of power.  I am making a small ground station to mount everything in.  This is not a directional antenna.  I get well over 1500 feet without pointing the RC at the P3.  I have not yet found the range limit.  I just sit in a chair with a small table in front of me,  set everything on the table and fly.  This does nothing for the video range,  but I have not lost the video yet other than what I mention below.

The loss of video signal I can get back by closing the DJI-Go ap.  Not just hitting the BACK button,  but actually closing down the app.  Then turn off the phone ,  restart it and load the DJI-Go ap.  That has worked so far.

As a counterpoint, i also happen to be using a GS5 on Android 5.0 with a P3S and have had absolutely zero issues with range or signal dropouts.  I haven't seen anything less than full signal strength at 1000+ ft.  I have no doubt that you have increased the range and signal integrity through your mods, but i think we should reinforce that a true range issue (drop outs at 100ft, 200ft, anything less than close to advertised range) should be addressed first through DJI support, before people start hacking up there RC's, because there may be some other issue with the RC that won't be fixed by amp-ing the 5.8ghz control signal.  

In clear space I can achieve 150m/500ft altitude with the drone 50m/160ft away from me. The video feed is extremely laggy at this point. I use the Sony Xperia Z2. The app then disconnects, and the Phantom will soon start descending or RTH until it picks up the signal again. Below 100m the video is fine. I don't trust myself to start modding the RC and dont think I should have to, i bought it in good faith thinking 500m would be enough distance for me but in reality i can't get anyhere near that without losing my connection so it's pretty much unsatisfactory.

Next steps for me:
Tru uninstalling some apps/ try flight mode on my phone
Try with my Girlfirend's Samsung S5
Try the windsurfer antenna
Get a refund and buy the Adv/Pro version

scottsmith10612 Posted at 2015-10-27 02:42
In clear space I can achieve 150m/500ft altitude with the drone 50m/160ft away from me. The video fe ...

Did u try to relink the drone with the RC?  I had signal lost in close distance with P3S after the firmware update; see my post about flight record.  Later a relink procedure seems have resolved the issue.

tdrussell1 Posted at 2015-10-26 13:54
As a counterpoint, i also happen to be using a GS5 on Android 5.0 with a P3S and have had absolutely ...

It's great that you are happy with your Phantom,  and you are certainly not alone.  There are lots of people who are thrilled with their DJI product.  However,  there is a growing number of people who appear to be having very similar problems.  The more information we can collect,  the more likely a pattern will be revealed that points to the possible solution.  In fact,  it would even probably be better if these reports included things like serial numbers,  what,  if any , mods you have done,  does the problem start right away at the beginning of each flight and get worse as battery voltage drops or things get warmer?  Really,  any information could be helpful.  Once you have enough data,  you can usually find the issue.  Possibly a minor change in a certain production run causes unintended consequence,  like a butterfly flapping his wings in Texas causes a flood in India.
As to DIY repairs,  well,  I bought my Phantom to use,  not to return to the manufacturer for repair.  Any product I purchase that has a problem I can deal with,  I will do so every time.  And for me,  the problem had an obvious solution.  In the immortal words of Scotty,  chief engineer on Star Trek,  " We need more power,  captain"

gongml Posted at 2015-10-27 17:57
Did u try to relink the drone with the RC?  I had signal lost in close distance with P3S after the ...

Yes I've tried re linking the remote a couple of times, resetting the compass etc, different battery etc. I just bought the Galaxy S6 and it's the same on that as my old phone.

I now have a case logged with DJI and have uploaded the flight logs so just awaiting their response. I'm highly suspicious of a dodgy transmitter.

scottsmith10612 Posted at 2015-10-29 02:30
Yes I've tried re linking the remote a couple of times, resetting the compass etc, different batte ...

Will be interesting to see what you come up with.  I rather suspect the receiver in the P3 in my case.

I had a same issue with the range.mine even not fly more than 50mts.If anybody gt the solution for that pls lets know.

Well mine is on it's way back to the shop. DJI confirmed it was covered by their warranty service and I can get an exchange or repair from the place I purchased it. It's a pity as I reckon if it wasn't so buggy I would have been very happy with it.

I'm still none the wiser what the problem is, and tbh I'm seriously looking at upgrading to the Adv/Pro version as I think going forward those will be the most bug-free versions. Hopefully I have better luck with the next one!