Thermostat or sending unit.
 

This one shouldn't be too hard, 2000 Tahoe Z71, 5.7 vortec, temp gage never goes much past 100* ,good heat coming from vents, Sending unit or thermostat? or just replace both?

Thanks

try the thermostat first. had the same prob with my 93 chev pu with 4.3 and also with my nissan sentra. thermostat fixed both of them.heaters work a lot better!you could borrow one of those laser thermoeters and just remove the rad cap and shoot the coolant and see what the temp is.that right there would tell ya.

Yep, changed the thermostat & now it's running right at 190*.
Thanks.