I have a 2000 f-350 super duty with a 7.3 power stroke and a 4r100 automatic transmission, the truck has 245k with the original transmission. while plowing snow the other day the trans. started slipping in drive, after another 100' or so like that, nothing. checked the fluid, a little low, no leaks, but reverse is fine. is this the end of the line for this trans?

 

Most likely yes. You may be able to get it to move forward after it cools down, but I don't think the trans owes you too much especially after plowing snow. It does place a good size demand on any automatic trans. Had a similar situation and after the trans cooled down it would move until it got hot then it gave up.