I would downgrade the baseband with redsnow 9.14b2 first. Open redsn0w choose extra-> select ipsw-> then select your ipsw (you'll need to download the ipsw for 5.0.1). Go back and click jailbreak. select only the option to downgrade baseband and then run the jailbreak. Then, with your downgraded baseband you have a few different options, you can either upgrade with iTunes then jailbreak again, or jailbreak with snowbreeze or redsnow. I would personally use snowbreeze (can download it here
http://ih8sn0w.com/) but it's just my preference. To do it with snowbreeze you will need to download snowbreeze and the 5.1.1 ipsw file. Open snowbreeze, select your ipsw file, click next. Choose simple mode if you don't have much experience with this program. It will preserve your baseband and create the custom ipsw file on your desktop. once this is finished, you will be given instructions to enter DFU mode. Then, open iTunes it will recognize the device as iPhone in recovery mode. click ok. Hold the shift button on your keyboard while clicking restore in iTunes. you will then choose your ipsw file that you just made (located on your desktop) Let iTunes run the restore, and you should be good to go. Also when the jailbreak is done, go to cydia and install ultrasn0w. Oh and I forgot to mention, you may have to run the baseband downgrade in redsn0w twice. It doesn't seem to happen often but sometimes you lose all wifi blootooth etc. If this happens just run the downgrade again same as first time and that usually does the trick for me. Let us know if you need further instructions.