You should go no lower than the 180 stat. You are stuck in open loop! The later trucks(like yours) are more picky about them so you may need to put the 195 back in.

 

Also get rid of the 165 stat...... The PCM expects to see 195, and it will whine if it doesn't. The 165 is probably also one of the reasons you are getting such crappy gas mileage. PCM is running the engine richer, as it thinks it should warm up more. In all reality, there isn't any real advantage to running a cooler stat on a basically stock engine. Stock cooling system is more than capable of keeping the engine the correct temp, even under heavy load.

 

Thanks for the information everyone. I got alot to change on this truck. I appreciate it.

 

Run the lowest octane fuel that doesn't deliver pinging. That's all octane does for you, prevent pinging and detonation, and once you've accomplished that going higher just reduces performance, fuel economy, and bank balance. (This isn't necessarily true on engines with knock sensors, but our engines don't have knock sensors.)