I have a 2000 f250 v10 that have been having issues with since I bought it less than a year ago with transmission and engine over heating. My current problem has been extreme hard shifting my OD light has been flashing and I’ve had loss of power when packing my car trailer up uphill with complete power loss I haven’t had any tranny fluid leaking out so I put an additive in it thinking maybe it was gunk build up causing issues and still no fix. I also put an SCT tuner in it that I can read tranny temp and it has stayed pretty low in temp. Any ideas on what could be going on before I take it in to have it serviced at my local ford garage

 

You have answered your question.... get the transmission looked at. The OD light being on points to the transmission. 200,000 miles V10... transmission. Backing trailer uphill and lose of power because of the stress on the transmission... imo