I am in the middle of a banzai run from Chicago to Fort Lauderdale, FL and somewhere in Kentucky the overdrive started to shift in and out. Sometimes it will stay in for 15 or so miles then start shifting again over and over. I am driving it with overdrive off and can only manage about 65 mph and am using too much fuel of course. What caused it and how to fix, any adjustments that can be made on the road? The truck also started idling very low too and will die when coming to a stop but not all the time too.