FINALLY!!!!!!!! so much old info on here, should really be redone. It was due to the old recovery, thank you! I woulda never figured that out.
HOW TO ROOT AND FLASH CYANOGENMOD 10.1 TO YOUR TMOB GS2 IN 2013!
Download latest 10.1 ROM and put on your SD card or internal storage
Download latest Google Apps/Gapps under the 10.1 column and put on your SD card or internal storage
If you're already on Android version 4.1.2 then you're fine, continue below, if not;
Download 4.1.2 stock rom
Tmobile GS2 Stock 4.1.2 ROM
1) “Extract” or “unzip” the downloaded stock ROM to get the .tar.md5 file
2) Run Odin3_v3.07.exe on PC desktop
3) In Odin - only check ‘Auto Reboot’ and ‘F-Reset’
4) Click on the PDA button then browse to the folder where you extracted the stock ROM “tar file”
5) Connect USB cord to phone and PC and boot into download mode. In Odin, the ID:COM box will change its color and its an indication that the device is connected properly to PC. If you still do not get any results, try another USB port on your computer.
6) Click the Start button to begin flashing.
7) Wait until it finishes or watch out for the word “PASS”.
Once the phone completely reboots, perform wipe/factory reset to get a fresher firmware installation.
1. Hold Power and Volume Up together, this will switch the device into recovery mode.
2. Release Power after holding it for a second but continue to hold the Volume Up button until recovery menu appears.
Select wipe cache
Select wipe data/factory reset.
That’s all! your Samsung Galaxy S II SGH-T989 now fully installed or restored to the original Android 4.1.2 Jelly bean
Ok, now that you're on 4.1.2, let's continue. The above step is also how to restore the phone back to stock.
Follow this STEP BY STEP noob friendly way to root, using the ODIN v3 provided above
Root Tmob GS2
Flash custom recovery
Download the TWRP recovery mode
TWRP 2.2 for Tmob GS2 aka Hercules recovery.tar.md5
plug phone back into PC and put in download mode
select the pda and select the recovery.tar file, hit start and let it finish
boot into recovery
wipe system, dalvik, cache, etc.
find your cm10.1zip and install
then find your gapps.zip and install
reboot, could take about 2-5 mins.