shakey 69 c-10

[tim1968]

my 69 c-10 has a shake at 55-65 mph it is a short box 2wd w\3 & 4" lowering springs it has all new suspension components new wheels & tires 3:08 gear ratio rebuilt th 350 w\ rebushed case new u joints the drive shaft has been rebalanced at DTS in ionia MI on recently recalibrated equipment, all drive angles are within 1 degree i have tried different wheels& tires changed rear ends also has new brake drums & brakes it is a in and out shake at consistant intervals any advice would be helpful thanks .. tim1968