How are you changing from 3/4" valves to 1" valves? Bushings? Red. ells?
If by going in to far, you mean it's not getting tight the threads have been cut too deep. Pipe threads (NPT) are tapered and should make up about 2-1/2 turns by hand...
If it's not getting tight no amount of pipe dope will keed it from leaking. It would be cheaper, and the correct way, to get another nipple, or whatever fitting you are trying to install....
I would also check the thread in question with another fitting to make sure the fitting wasn't split or defective like another poster stated....