Hey dude - I just finished fixing my bluetooth issues and might be able to help. You say it was working fine for you previously? No problems pairing? No issues with auto-connections? Then, suddenly, it stopped? It didn't stop after a software upgrade? Or, after installation of a new app/mod?
For me, everything was perfect one day...then ZERO. Changing ROMs had no effect - I did just about everything to rule out a software issue. Before I brought it in for service, I wanted to try a fix myself.
First thing I did was pop off the back cover. Then, with a small screwdriver [flathead], I gently [GENTLY!] lifted the tab-connectors so they were raised a bit more. These are all of the contact points - where the cover contacts the device - and if they are not making a solid connection, then things are going to get messed up.
After lifting the tabs, try putting your back cover back on, taking special care that it is seated properly. Looking at the back of the device, if you run your eye along the seam above the kickstand [where the bottom of the cover is], that should be perfectly flat. I've seen the back cover not seated properly and that cause the bluetooth problem. You'll notice one side of that seam is ever-so slightly lifted.
OK - so that's the back cover.
If none of that works, you can decide to go to Sprint [they will not give you a hard time because the device is rooted - other users can confirm] or you can open the device up to tighten the screws yourself. All I really did was unscrew a few pieces, then tighten them back down.
To be honest, I can't tell you if it was my work on the back cover or the tightening of screws that resolved the issue for me, but it's been working perfectly since. It's been a couple of weeks, I think, since I posted about it...bluetooth auto-connects as soon as I sit in my car, and it stays connected...no problems.
One more thing to note. When my bluetooth wasn't working, I was able to "coax" the device to pair/connect by pressing with my thumbs on the back cover [in the area just below the camera] - sometimes, I needed to run my finger across the top of the kickstand [back and forth a few times until it paired/connected]. Doing some physical manipulation of the device, I was able to get it to work...so I knew the issue wasn't software, but rather a lose screw or bad connection between the cover and device.
...have fun with it!