autometer temp problem

[goob8869]

I have a 67 Camaro with a ls6 in it with autometer gauges. After about 6 to 7 min after starting the gauge is reading around 250. I changed tstat and checked water pump both was working fine so I shot the tstat housing and heads with a laser temp gun and it read 100 at tstat and 110 at heads. Is this a sending unit, gauge problem, or something else. The gauges and sending unit are practically new. Any help much appreciated