Mocoman

I had the same problem myself with several mod packs that were big enough to leave my computer with "no memory". The way i fixed it was by going to Java and downloading the x64 version offline. This allowed me to go to the Tekkit launcher options and change my memory allocated from max 1 GB all the way to my 8 GB that my ram has to offer. The reason why many people have the server shutting down error is because if they are running x32 java no matter how much ram you have it will always only allocate 1 GB so most mods will not load fully before your memory is full, leading to failure. Once I dowloaded the x64 offline and changed it all the way to 6 GB of memory it loaded perfectly and had no more "missing chunks" that you could see past bedrock. Your windows system or whatever system you have must be x64 for this to work. Go to your settings/system/about (all the way at the bottom on windows 10) and then system type. If it says x64 go to https://www.java.com/en/download/manual.jsp and click the x64 offline. Once you dowload it (and uninstall the latest version only if while installing java asks you to) then you can open tekkit launcher go to Launcher Options on the Top right corner (Not modpack options)/Java settings/ Memory and change it to whatever value you want. I wouldn't do maximum so your computer runs smooth but also not so low that it doesn't solve it. In my case 4-6 GB worked just fine. Hope it helps. GL.