What material are you threading? Are you using a 1 inch round adj die? Is it High speed steel? What are holding the die and tap with?
I would cut the tenon .348 and drill the hole 8.3 (.327) for my normal threading of that size.
If you have an adj die it may be closed to much and cutting the threads to small. It may be your shearing the top of the threads on the tenon. Pictures of your set up and results would help.