Arkie_3_fan

My dad's 1992 Extended Cab V-6 4x4 has developed some transmisson problems this summer/fall.
I've done some searching on this site and others but haven't really come across a similar problem.
The problems started as he was hauling small trailer load of firewood home from the woods. He noticed it slipping and he nursed it a couple of miles but parked it at the base of a hill and then towed it home.
Once home, he drained the fluid and refilled it. The truck drove fine with no problems. Then later he went to get in it and it wouldn't go anywhere. After looking, he found one of the hoses was leaking, so he replaced that, added more fluid and he drove it around the house and field for a week with no problems.
Finally, he ventured out for another load of wood. Made it home, unhooked the trailer and parked the truck. An hour later he returns to his truck, fires it up and it won't move out of it's tracks.
Since then, he's tried it about every day or two for the past few weeks and every few days the truck will take off when you shift into gear, but most days it won't do anything.

Could it be a solenoid going bad and only working every now and then?
Maybe a sensor or switch somewhere?
I'm hoping for suggestions on anything we need to check on it. We sure don't want to have to take it to a tranny shop or buy a used tranny ($900 from the local salvage yard) if we can fix it ourselves.

Arkie_3_fan

Well, it fired up and took off yesterday afternoon. Drove all over my grandma's land and returned home. Turned it off and 10 minutes later it wouldn't leave it's tracks. Crazy truck has a mind of it's own.