2007 135D Deere Cooling sytem

We have a Deere 2007 135D with a Isuzu engine with a cooling system problem, After about 15 min run time, the high temp alarm comes on, also the temp gage goes into the red & derates. Changed out thermostat, lower temp sender & sensor still did it, Deere tech checked it out, said water pump was shot not circulating coolant, so changed out water pump, the old pump had lots of end play & up & down ,flushed rad, put it back together same problem, alarm and gage says it getting hot,but put temp gun on its around 75 c. Replaced high temp sender, problem went away, 2 days later its back, confused , could it be the temp gage & monitor ? What does the 2 senders and sensor on the thermostat housing do, I am old school so this is all new to me, have ordered a tech manual but its take a couple of weeks to get. Thanks in advance for any help, Ken

2007 135D Deere Cooling sytem