My wife came home and complained about truck not going into gear. Ion inspection, the trans is making a loud noise. I topped off the fluid and now the noise stops when the truck is moving but still loud when idling. Any help would be a

 

No vehicle info provided.

 

My mistake. It is a 2004 excursion with the 5r110 trans. Three years ago I removed the 6.0 and replaced it with a 12,valve cummins

 

How hot is the Cummins?
The 5r110 is a great transmission and all, but in stock form the ECU does defuel the engine slightly before a shift. With a mechanical 12 valve in front of it, that’s no longer happening and the trans is shifting under full engine torque. If the Cummins is fairly mild, shouldn't be a problem, but if it’s a pretty hot built Cummins that’s putting down serious torque, that could cause an issue over time.
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Sounds torque converter ish to me, maybe its damaged but still working.