Engine wont rev up?

I have a New Holland 555E hoe with 4800 hrs. All filters were changed at 4700hr, the machine was running fine in the fall. It sat over the winter, fired right up the other day and ran great. After a few minutes the engine wouldn't rev up, in or out of gear. There was a hot smell almost like clutch plate. I shut it down right away, have looked for obvious things like critter nests etc. There is a little crud in sediment bowl, but other wise nothing obvious. Appreciate any help.