my new 306 has a very odd vibration 2800 and above and gets worse the higher the rpm upto 4500 (that is the highest Ive let the rpms go) it does it free rev or driving, I have also swaped in a c-4 with the 50 oz flexplate the crank # shows to be out of an 87 truck, any pointers please, would anything ignition wise or fuel systeme cause this.... looking for somthing simple preferably.....I can wish right.