New Thermostat - How long to warm up

[MosH]

Ok, so the SES light came on this past Saturday, brought it to my mechanic and the code was for a stuck open thermostat. This made sense since on my drive there (20mins ont he highway) my temp guage never came up to 12 o'clock (was always running cold). So the quote was 230 for a new thermostate andhousing with full coolant flush, fair price. I picked it up yesterday evening, on the drive home the guage stayed at 12 o'clock the entire time (truck was already warmed up when I started it). I left it in front of the house for about 6 hours in 40 degree temps. I took it out again, drove about 5mins at highway speed, let it idle for 5mins in a parking lot and drove back 5more mins at hwy speed, the guage never came up to 12 o'clock and actually was going down at bit on the hwy. This tells me the thermostat is still not right however Im not sure how long this truck takes to warm up. Can anyone shed any light? Did I just get a coolant flush and no new thermostat?