Massive packet loss on non-stock roms

I hope someone can help me, this is driving me up the wall.

I've got a t0lte. I've been using the H3G image for it for a few months, with no problems with the network apart from not going onto LTE, and massive problems with Bluetooth (it seems Samsung suck at it). So I installed OmniROM 4.4.2. After a few days, I started getting up to 50% packet loss. I switched to CM11, same thing. Then on to SlimKat, as someone on #omnirom suggested it might be the RIL, but it wasn't that. I tried two other modems, didn't help. I then tried OmniROM 4.3.1, same thing, and CM10.2, same thing. Tried the latest modem I could find, XXUENA1, same thing.

People have suggested it might be a carrier issue (I'm on H3G), but I can't fathom how. I don't experience any packet loss on the stock H3G image I downloaded. But now they are rolling out LTE, I need something that can get on it.

I've hunted through the interwebs and can't find anything matching this.

Can anyone help?

Steve

I've been doing some further investigation, and it seems as if what's happening, which might be the cause, or a symptom, is that it's switching between HSDPA and DC-HSDPA constantly. I'm not sure if that switch is a function of the firmware, or something on the mast side, can anyone offer any advice/experience on that?

Ta

Steve

Ok, I tried the MB2 modem from http://xdaforums.com/showthread.php?t=2031575 , but that didn't make any difference. I also tried changing one of the build.prop settings for the downswitching, and that didn't work either.

Anyone got any ideas? I really don't want to be stuck on the crappy Samsung software