A long time ago, I worked on a Hardbody V6 4x4 with an auto trans that had a similar problem. Cold, it would start up and drive fine, but after going a few blocks, it would start slipping bad and then go nowhere. Turn it off and let it sit for 30-minute or longer, it would move and eventually do the same thing. The problem turned out to be a clutch pack was failing and allowed a lot of fine clutch lining material into the fluid. As the vehicle ran, the transmission pump would get fluid starved as the filter screen would get clogged by the debris in the fluid. When the vehicle was turned off, the debris would fall off of the screen back into the pan. Next time the vehicle was started, there was enough fluid getting through the screen to the pump until it eventually got clogged, again. You would verify this is the case by using a trans oil pressure gauge to check the line pressure. Full or close to full line pressure should be seen immediately after a cold start, but it would start dropping in pressure as the vehicle is driven or run. If that's the case, the transmission would have to be replaced or rebuilt. If rebuilt, the case and internals would need to be thoroughly cleaned to make sure the fine clutch lining debris is totally removed. Also, if this is the case and the transmission is rebuilt or replaced, I would highly recommend replacing the radiator as the fin-type trans cooler inside the radiator could get contaminated and restrictive because of the debris.