OK looking at your logs I'm seeing this:
[06/8/2014 13:43:11 PM] [Client thread/INFO] [inventorytweaks]: micdoodle8.mods.galacticraft.core.client.gui.screen.GuiCelestialSelection
[06/8/2014 13:43:18 PM] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 8022ms behind, skipping 160 tick(s)
[06/8/2014 13:43:19 PM] [Server thread/INFO] [Galacticraft]: Found matching world (-30) for name: Asteroids
[06/8/2014 13:43:19 PM] [Server thread/INFO] [Galacticraft]: DEBUG: Attempting to remove player from old dimension 0
[06/8/2014 13:43:19 PM] [Server thread/INFO] [Galacticraft]: DEBUG: Successfully removed player from old dimension 0
[06/8/2014 13:43:19 PM] [Server thread/INFO] [Galacticraft]: DEBUG: Sending respawn packet to player for dim -30
[06/8/2014 13:43:19 PM] [Server thread/INFO] [FML]: Testing asteroid at x10 y199 z72
[06/8/2014 13:43:19 PM] [Server thread/INFO] [FML]: Found asteroid at x10 z72
[06/8/2014 13:43:19 PM] [Server thread/INFO] [Galacticraft]: DEBUG: Loading first chunk in new dimension.
[06/8/2014 13:43:22 PM] [Client thread/INFO] [inventorytweaks]: net.minecraft.client.gui.GuiDownloadTerrain
[06/8/2014 13:43:22 PM] [Server thread/INFO] [Galacticraft]: Server attempting to transfer player **MINECRAFTUSERNAME** to dimension -30
[06/8/2014 13:43:22 PM] [Server thread/INFO] [Project Red]: Created Retrogen database for dimension -30
[06/8/2014 13:43:22 PM] [Client thread/INFO] [NEIAddons]: World changed, resetting
[06/8/2014 13:43:22 PM] [Client thread/INFO] [NEIAddons]: Available server commands: SetForestryWorktableRecipe
[06/8/2014 13:43:29 PM] [Client thread/INFO] [inventorytweaks]: net.minecraft.client.gui.GuiChat
[06/8/2014 13:43:30 PM] Now reading data segment for mismatching mcversion: Minecraft 1.6.4
[06/8/2014 13:43:30 PM] Now reading data segment for mismatching mcversion: Minecraft 1.7.2
[06/8/2014 13:43:30 PM] Your mcversion is: Minecraft 1.7.10 and matches the next Update Checker data segment
[06/8/2014 13:43:30 PM] IC2 Advanced Machines Addon was found up to date by Update Checker
[06/8/2014 13:43:39 PM] [Client thread/INFO] [inventorytweaks]: net.minecraft.client.gui.GuiChat
[06/8/2014 13:43:40 PM] event
Here are my comments:
* the Galacticraft code appears to be working correctly according to the DEBUG lines and the FoundAsteroid line - that is 100% normal
* you have major lag where it logs "Can't keep up! Did the system time change, or is the server overloaded?" - when I say "major" lag I mean horrendous, like everything literally stopped for 8 seconds - it was even worse in your other log
* I'm seeing InventoryTweaks logging around the position of the lag so it could be something connected with that
* You have some kind of other problem with these spammed messages about "mismatching mcversion: Minecraft 1.6.4"
* You have repeated errors from SteamCraft.
I'm not really willing to spend more time trouble-shooting this when you have other mods reporting errors. I strongly recommend you make a thinned-down modpack which includes only Galacticraft and one of the power mods and NEI, and test with that. (Not InventoryTweaks or SteamCraft obviously, as those could be connected with the lag. Also not Forestry.)
If the thinned-down modpack works without these dimension teleport errors, then start adding in other mods, and see if you can figure out which one makes the problem start happening again.