340 Overheating Help

I ran it tonight with a sun gauge i bought from pepboys. Its reading a solid 180 degrees.

It's the gauge in the dash that is the problem, i'm thinking the sending unit. I installed a new sending unit when i installed the motor. The dash gauge is on the hot bar, and the sun gauge is at 180.

It still will not start hot, but i think there's something wrong with the starter. Thanks for all the pointers and tips. This forum is the best!