I dont know if one thing has to do with another, I just replaced alternator yesterday and had to go out of town today. At highway speeds 55-70 my truck would jerk really hard for a split second and then run fine. happens like once or twice in a row every couple of min. rpm guage does not fluctuate when this happens. checked tranny fluid and its fine. Did I get some bad gas or tranny going out? suppose to go out of town tomorrow but I dont want to get stuck in the middle of nowhere. thanks for any help.