I have a ford 655c backhoe and when I hopped in it, it was completely dead. After charging the battery the engine fired right up and I let it idle for about 30 minutes before driving to my work location. The backhoe made it 100 foot in second and just stopped moving forward no noise or anything. I could not get it to go forward or reverse in any gear. So I shut down the engine and went to start it back up and it was dead again. After jumping the battery and letting the tractor idle again for 30 min. I started driving with no problem. After driving in second for about 5 minutes half throttle the darn thing did it again but I could use reverse for one try until I put it in neutral again then of course I had nothing and had to tow it back to the barn. I am not to familiar with working with this piece of equipment and I would like to note I am picking up the scraps on someone else's neglecting work habits. I looked around and could not find anyone with a related problem. I'm thinking it is probably the electric clutch but I would like some advice before tearing into this thing because I don't need another endless project like my two sicards that need "re-engineered".
Is the alternator charging? Check the voltage idling and driving also. No clue what's in your transmission, but that sounds like a logical and easy place to start.
It would be a good idea to take a look at the shuttle shift control before tearing into the transmission. You need to confirm that its sending voltage to the shuttle.