I have a 99 blazer and was wondering if I could run a 160 on my truck or do I have to have a 180?

 

Neither. Use a 195 degree thermostat unless you want your engine to stay in open loop operation and let your gas mileage and power suffer.

 

So run a higher one?

Would it make my motor run hoter?

 

Engines that are computer controlled require higher heat to operate correctly. 195 degree thermostats are normal. Anything colder will do as explained above. Gas mileage & overall performance will be affected for the worse.
These engines need to run hot (210-220 degrees.) That is one reason anti freeze is important to use instead of water as in the old days. Because a 50-50 mixture of anti freeze & water raises the boiling point several degrees above 212 degrees of plain water.