Dash gauge readings

[bigd65]

Ok so I got all my wiring problems fixed and the gauges working, however they are not reading correctly. The oil gauge is reading a little high, not bad but I know the oil pressure on these trucks don't go real high, that's just a Chevy. The temperature gauge goes way over to hot. I changed the thermostat and flushed the engine and new coolant and all. However the temp still goes way to hot and then slowly drops a little. The engine is by no means hot in fact you can actually put your hand on the valve cover. I'm thinking it's just the wrong senders or something. I got the ones for the diesel that it was originally but then again I did change the cluster and its now a gas 350, however they showed the same part numbers for the diesel and the gas engine for the same year

How can I tell what senders I need to buy, is there an ohm reading I can take from the gauge or something.
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