Hi everyone this is my first time on here.I have a 57gmc Napco truck I picked up from the west coast this fall.I like the body style.The crome on the front off a 56.The engine is a 327 with dual exhaust.Four speed with granny gear.The diff gears I think are 3.90.I would like a better hiway gear.In 4th at about 55 Im at 2300rpm.I would like lower rpms.The front diff has Napco on the diff.Any help would be great. Thanks