It almost sounds like you might have boogered up the internal lining (Teflon) of the outer sheath and then hanging up the inner cable when you try to insert it through. I've used several of those throttle cables in the past plus now their cruise cable and kickdown plus the e-brake cables with never a problem. I'm using a solid throttle rod instead of a cable now which might be an alternative.

If you call Lokar, they might feel sorry for you and sell you a replacement inner cable fairly reasonably - they have even given me various parts when I've had problems