I just finished rebuilding my straight LS motor, I replaced every single hose, new head gasket, resurfaced head, and new head studs.

My problem is that the motor seems to only overheat when I'm driving continuously without breaking, like when I'm on the freeway going 60 for about 5 mins, the temp would go over half way. I would have to slow down then the temp drops. I'm thinking it's the thermostat and just wanted to see what else it could possibly be.

My radiator or cap seems to not be working properly also. After the car overheats half way up the gauge, I stop and I can hear steam leaking from the cap... is this normal? I also noticed that the radiator neck where the cap goes on is damaged. I can turn the cap all the way around without stopping. If the neck is damaged, do I need to replace the whole radiator? Or do you guys think it's just the cap?

BTW: All this happened last night and to fix the leak from the cap, I used some liquid gasket on the cap and I don't hear any more steam from it. Doing this won't damage anything right? Because my girl took the car to work this morning.