My 96 Ram 3500 5.9 Cummings is kicking out gear once operating temp is reached. The odd thing is that the oil pressure light illuminates, the gauge drops, and the brake lights illuminate, The only current work on the truck was replacing the vacuum booster and master cylinder. Nationwide transmission is trying to say the transmission is fine and the problem is the truck. I not sure what that means, but I believe, that a transmission not maintaining clutch pressure weather electrical or pressure is a transmission problem.
Anyone have any ideas as to what could be causing this?

 

It does sound like you have an electrical gremlin, which on a 28 year old Dodge isn't surprising. If all that is indeed happening at once I would check into it. That is a 47RE so there is a fair amount of electrical control happening, I'm not knowledgeable enough on how they work though to speak for that. I though you were still mechanically/hydraulically engaged in forward and reverse ranges up to 3rd but I'm not positive. A fluid level check would be a good idea as well as inspecting it. I would recommend a fluid change/pan drop for inspection but sometimes its nice to get to that point in diagnosing before just doing it. You can wash away alot of evidence and alter the scenario.