Running cool

This is my second posting, first got good results with a good fix. Anyway, this problem is that my truck is running too cool. Even in 95° sunny weather down the highway or city driving the gauge runs anywhere from 140° to 180°, usually at the 140° mark.

It's a 94 1500 w/5.7L and 201000+ miles. I've replaced the thermostat with a 190° one, fan clutch (old one was worn out anyway), and the temperature sensor. It wouldn't bother me except that I'm afraid it would overheat and I wouldn't know it until too late.

The only other thing I haven't done, that I know of is to test the accuracy of the gauge, but haven't gotten around to it yet.

So, any other things to try that I might not have looked at?
Thanks a bunch....