My 95 in sig has developed a vibration between 1400-1700 under load. It isn't a shaking vibration but you can really feel it in steering wheel and on floor boards. Checked all u-joints and yokes and had one that was a little loose so I replaced it but no effect. It also seems to miss a little under load but idles fine. This started Sat morning and that morning truck had a erradic idle but since is fine. Could an injector cause a vibration?