I was doing some highway cruising over the past few days. Everything is working great that I know of except when i get up to speed of around 55mph there is a slight vibration/shake but if I keep accelerating to about 60/65 the ride smoothies out to buttery smooth. Rig is a 77’ FJ40, fresh rebuilt engine, transfer case, transmission. Fresh front axle rebuild. Drivelines were freshly balanced. Tires were balanced when mounted via a road force balancing machine. Wheels are stock steel, tires are 35/10.5/r15 It drives smooth all the way up to 55, then is “shaky” between 55-59ish then smoothes our right around 69. Steering is electronic power steering and I tried it with the power off, mild assist, and high assist. Same thing.. What am I not thinking of? Pic was taken today on my way back to Nevada from the wine country.