engine running cooler than usual?

[bass_caster]

2000 nbs 5.3l 225,000 miles

over the last week or so i noticed the temp gauge on the dash has not been reaching the "normal" operating temp its been running cooler than normal, atleast according to the dash gauge, even after lengthy drives. my initial thought was a thermostat stuck open.

over the same time period it seems to be burning more gas

if its not reaching full operating temp would it run less efficiently and burn more fuel?

i'm overdue to replace the slow leak water pump so the thermostat is an automatic replacement anyways, i just dont know if i need to be looking for something else.

thanks