Yeah, you have some sort of big vaccuum leak somewhere. Check all the hoses too, but if the intake is leaking at the upper to lower gasket, it could be revving up like that too. I've seen that very same thing happen, and it was a vac hose that had fallen off when we were installing a new engine.
checked all my vacume lines i am leaning towards upper intake the gasket was made with gasket maker i have to order that gasket do you think i should just put stock back on to check this motor was just built