Yet another post to thank you guys and increase the likeliness of someone else finding this answer to our problem !
So, as others here, after updating to the great Pershoot's build of Android Jelly Bean 4.2.1 (from droidbasement.com) for my Galaxy Tab 10.1 WiFi P7510, I encountered the problem that the screen was flickering / rolling (as if the sync was wrong) every time the the tab was woke up from automatic sleep or manual lock, thus forcing me to reboot it every time or disabling the automatic sleep...
I followed the instructions from davinchi27, that I will refine some more :
1) Go to droidbasement.com
2) Go into the files for CM10 p4Wifi, i.e. http://droidbasement.com/galaxy/roms/cm10.1/p4wifi/
3) Download "US_LPL_4.0.4_bootloader.zip" and extract its content
4) Download "recovery.tar.md5"
5) Download ODIN (I got a version that seemed recent enough (1.85) from http://forum.xda-developers.com/show....php?t=1651794
6) Go into download mode in the tab (IIRC, reboot with power + sound -)
7) In ODIN, check "Auto Reboot" and "F. Reset Time" but not "Re-Partition" (should be the default)
8) Click on BOOTLOADER and load 4.0.4_bootloader.tar.md5
9) Click on PDA and load recovery.tar.md5
10) Start the flashing process
EDIT : looks like flashing recovery.tad.md5 (I guess) changed the ClockWorkMod (CWM) from the touched based version I had bought to some non touch based 126.96.36.199 one, but this isn't flickering there either, so I'm fine ! Maybe this file should not be flashed and only the bootloader should be...
Once again, thanks to you all !!!