Still having the same issue after dealer repaired the truck 1.5 years ago. Trans wouldnt go into o/d and flashing o/d light. Dealer replaced shift solenoid pack and flushed trans and put new ATF and filter in. 2 miles later had o/d but light was still blinking. Took back to dealer and they said new transmission. Refused and delt with it. Changed alternator 3 months later and problem went away. 6 months later o/d flashing again. Changed alternator again and problem still existed. Delt with it till last week when I figured the ts performance chip might be causing it. Removed and bought a edge cts instead. O/d still blinking. Was told to recalibrate the PCM might fix it. Had that done today. O/d light still blinking. Later this afternoon thought the Chinese alternator might be at fault. Bought a new one from ford. Still have flashing o/d light. I only get the light under light acceleration. Driving hard is fine. Towing any load is fine. Even 10,000 lbs. no slipping at all. I'm confused????

It's late to shift from 3 to 4. I can watch it on my edge cts the PCM commands 4th and the truck goes into 4th 5-7 seconds later on light acceleration.

 

That code means the 3-4 shift isn't happening when the PCM commands it. You already knew that's what is happening.

There are several reasons this could be happening. All of them are inside the transmission.

 

So it's not an electrical issue? It's mechanical/hydraulic?

Could It be a sticky valve.

 

Well when the PCM commands 4th and it won't go into 4th if I gas it just a little and quickly the it goes right into 4th without a problem. Sounds like a weak pump but that would cause all gears to shift late? Right?. Could it be something wrong with the valves in the valve body? Ordering a John woods valve body next week.

 

It's not a weak pump, that would affect everything. It could be a sticky valve, it's most likely a bad seal in the overdrive clutch.

 

So bad seal in od clutch means total rebuild basically.