engine vibration

i installed a remanufactured 1974 302 in my f-100. i purchased a 28 oz. flexplate and a 28 oz. fluid damper for it because of a vibration problem i had with the previous engine between 2000 & 3500 rpm. now when i fire up the new engine it has a worse vibration in the same rpm range and smooths out above 3000 rpm. could it possibly be my aftermarket torque converter? i put it in with the first engine and i am not sure but i think that is when my trouble began. please help !!!!!!!