Kaji Kaldaka

I've been using Tekkit for a few days now and I've noticed that for whatever reason, my vanilla powered rails are no longer powerful. They create such a lack of acceleration even 2 powered rails every 30 blocks struggles to make the trip. It never does this in vanilla. I've tried disabling Railcraft (And the NEI plugin), but it still didn't change anything. What other files should I get rid of? I'm not using much of Tekkit itself, but I certainly don't mind disabling a few mods for now. PS: While I'm at it, why does the launcher only show the default skin, not my custom one?