Engine running hot
 

I have what I believe is a 228 cid inline six in a 50 GMC 1/2 ton 3100
that is running hot in the back half of the engine. The front seems to be cooling alright. The temp sending unit is located towards the rear of the engine and is showing 220 plus degrees, (verified by a infrared hand unit). The front half of the motor is running around 185 degrees. It has a 160 thermostat in the water neck and the electric fan goes on at 185 degrees.
Has anyone had this problem? Any help would be appreciated.

Thanks