no o/d flashing o/d light

[mnichols2010]

4r100 won't shift at all won't even try to go in o/d and the o/d light has been flashing ever since i had the trans rebuilt which was only maybe 5000 miles ago all gears worked just fine until i stop to fuel up and jumped back on the highway and no 4th i don't have a code reader of any kind don't want to deal with a dealership or the backwoods fools who rebuilt my trans trans fluid is fine no leaks temp is always about average but i was pulling a 05 dodge dakota on a 18 foot trailer and my trans temp pegged out at 250 and stayed there for about 2 hours any ideas are greatly appreciated.