Truck has 175k miles on it and has always ran great and shifted perfectly. A week ago while going from one highway to the next it just spun up in overdrive as if a shift solenoid gave out. I slowed down to a stop on the shoulder and took off again and it was fine till it shifted into 3rd and spun up again as though the gear was gone. Shifts fine from 1st to 2nd. The only other symptom is that with the overdrive button turned off it drives fine in 1st and 2nd and never tries to shift to 3rd or O/D which I find odd and if I have the O/D on and it tries to shift 3rd isnt there, push the O/D button and it locks into 2nd and you can drive it. It manually shifts from 1st to 2nd as well, but go to drive and nothing after 2nd.

I did replace all solenoids and put new fluid and filter in it and I found the little plunger / plug in the pan so the pan has never been off the truck before. There was a fair amount of shavings on the magnet but no more than I have seen on quite a few transmissions with some miles so not enough to scare me and the fluid does not smell burned, just used. Any ideas? I have no Check Engine lights of any kind but have not had anyone run codes.

This is a 2006 Lariat 4x4 with 5.4L 3V and 4R75W automatic.

 

You have a direct clutch(3rd gear) problem. Since it happened suddenly I would guess the weld broke in the drum. No way to know for sure without tearing it down. Its trying to shift to 3rd but stays in second because the clutch isn't applying. 2nd stays applied in 3rd and 4th but the intermediate one way overruns when direct is applied. It neutralizes in 4th because the forward clutch releases and the OD band applies but the direct isn't holding.

 

I assume this is not something that can be fixed without someone opening up the tranny case? I am not afraid to pull the pan and poke around but disassembly of an automatic is beyond my pay grade.

 

Before you tear the whole transmission apart, I'd pull the valve body off and check the Overdrive servo piston pin fit in the case. You can seperate it from the piston and wiggle it in the hole. If you can make it rock in the bore, the bore is worn out. If this is the case, Sonnex has a pin with an O ring that should help. Also check the valve body plate to make sure it isn't warped. After 2002 a strengthening plate was removed, and this causes leakage problems too. Easy to check before pulling the whole trans.