Hitachi EX100-3 Engine loading up

Hello all and thanks in advance for any help. Its a 1998 grey machine. Yeah I know, 1st mistake. Bought it with bad pump and had it rebuilt at trusted shop. All functions slow and engine loading up. Took it to John Deere dealer, 2nd mistake. They adjusted angle sensor and helped with speed of functions but engine still loading up. Fuel system cleaned, pump and injectors rebuilt. Still loading engine. I think must be a sensor not working properly. They say they don't know what to do ( go figure ) and think its pump. Any suggestions what to look for? I really need to close the money hole on this thing and get it to work. Been dealing with this for 6 months and am about ready for mental institution