1995 Chevy tahoe problems thermostat?

[Shawn]

I have replaced water pump ,thermostat,and sensor . it is a 350 . before i put new stuff in the inside gauge was around 200 , after i replaced all the stuff it (inside gauge) went to 235 to 240 . I called chevy and they said it should run at 195 to 200, but it put a thermal temp tool on block and it is at 210 to 215. Now here is why i am confused without thermostat in the temp on gauge read 195 to 200 , but just as soon as i put the thermostat back in it shoots back up , i removed all the air and flushed system . I ran it for a good while and it does not go to 260 which is the overheat point on gauge and no warning lights come on .I put three thermostats all new all did the same thing . So my question is could my inside gauge be bad , and if not what should i do put a 160 degree thermostat in rather the 195 ? Could i hurt my engine at these temps everyone I talked to is confused and i to am ?????? Thanks for any help on this