Seeing the same issue with DNS TechPack. When you reach a height of about 180-190 it bombs with that payload 32k error.
The coders over there are saying its a Forge Bug.
[17/9/2014 19:09:13 PM] java.lang.IllegalArgumentException: Payload may not be larger than 32k
[17/9/2014 19:09:13 PM] at net.minecraft.network.play.client.C17PacketCustomPayload.<init>(SourceFile:38) ~[iz.class:?]
[17/9/2014 19:09:13 PM] at cpw.mods.fml.common.network.internal.FMLProxyPacket.toC17Packet(FMLProxyPacket.java:120) ~[FMLProxyPacket.class:?]
[17/9/2014 19:09:13 PM] at cpw.mods.fml.common.network.handshake.NetworkDispatcher.write(NetworkDispatcher.java:417) ~[NetworkDispatcher.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.invokeWrite(DefaultChannelHandlerContext.java:644) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.write(DefaultChannelHandlerContext.java:698) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.write(DefaultChannelHandlerContext.java:637) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at mods.immibis.core.impl.NetworkingManager$FakeSpecialPacketHandler.write(NetworkingManager.java:482) ~[NetworkingManager$FakeSpecialPacketHandler.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.invokeWrite(DefaultChannelHandlerContext.java:644) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.write(DefaultChannelHandlerContext.java:698) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.writeAndFlush(DefaultChannelHandlerContext.java:688) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelHandlerContext.writeAndFlush(DefaultChannelHandlerContext.java:717) ~[DefaultChannelHandlerContext.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:893) ~[DefaultChannelPipeline.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:239) ~[AbstractChannel.class:?]
[17/9/2014 19:09:13 PM] at net.minecraft.network.NetworkManager$1.run(NetworkManager.java:174) [ek.class:?]
[17/9/2014 19:09:13 PM] at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354) [singleThreadEventExecutor.class:?]
[17/9/2014 19:09:13 PM] at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:348) [NioEventLoop.class:?]
[17/9/2014 19:09:13 PM] at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) [singleThreadEventExecutor$2.class:?]
[17/9/2014 19:09:13 PM] at java.lang.Thread.run(Unknown Source) [?:1.8.0_11]