555E motor bogs down and will die.

I have a 555E backhoe. When I would dig or use the front end loader the motor would bog down and some times die. It's and older unit and was smoking so I had the motor rebuilt. When I got it back it was still doing the same thing and the transmition went out. Thought that might have been the problem. Had it rebuilt and it still doing the same thing. It seems to bog down when in gear and using the hydrolics. Any help would be appreciated. Thanks

555E motor bogs down and will die.