FWIW Mechanic came and removed the valve cover and sure enough there was a bent push rod. (Cat 3126 engine) Seems to me that you should be able to slow down quick with the Hydrostat without messing up yor engine. But anyway it runs fine now. So the moral of the story is -for you rogator operators out there-, beware that a sudden slow down when skooting down the Highway at 30 MPH is not a good idea.  }:o( 

The exhaust brake is working now but I am not sure how effective it is cause I am afraid to back off the hydro real fast to find out.