Intake manifold torque

I think you said "'hardware grade 5". I hope those are not from any hardware store. Only automotive grade fasteners are designed to be used on autos. Rolled threads, specials shoulders etc...
What type and quality of torque wrench are you using ?
Magnum intake torque spec is 2 step. First to 16 lbs. Then torque to 23-25 lbs. This is with a Magnum bolt pattern intake.