Are your tires round? large diameter and out of round will cause it to hop. It might be the road also, my '57 rides well, my 2011 2500Hd crew cab 8 ft.bed will bounce you out of the seat on certain seamed concrete highways. Wheelbase, tires, suspension, road surface will all have an effect.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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