When truck is up to operating temp, overdrive does not work and the alternator only charges 12.3vdc. I change the alternator out with a new (not rebuilt) unit.NO CHANGE. Not worried about charging system!!! I travel 40 miles on the highway to work. No overdrive and 4.10 gears means I am a road hazard and late to work. HELP!!!

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This issue started a while ago, but in the beginning, it was only if i let it idle for 15+ minutes. And then after about 2 miles of driving, it would return to normal... Now, it is all the time. If I can get into overdrive, it will work great until I slow down enough for it to drop into third, then im screwed...

 

Check your crank sensor connections? Is it clean and is the gap correct, .050 checked with a NON ferrous feeler gauge or a matchbook cover folded over. Outside of that I got nuthin'. Good luck!