No engine heat!

My 1st post here.
99 4wd The outside temps been 0-15 degrees.
My engine temp isnt reaching 100*(according to my dash).
I warm the truck for 20 minutes before I drive it ,and the temp never goes up.
I also think this is causing my heat to not get very hot..just above cool below warm.
Whats my issue?
Bad thermostat?
Any links to removal?
Thanks!
CS

Your Thermostat is the first place I'd start at, also do a Reverse flush on the heater core.

My 1st post here.
99 4wd The outside temps been 0-15 degrees.
My engine temp isnt reaching 100*(according to my dash).
I warm the truck for 20 minutes before I drive it ,and the temp never goes up.
I also think this is causing my heat to not get very hot..just above cool below warm.
Whats my issue?
Bad thermostat?
Any links to removal?
Thanks!
CShad the same problem,replaved the thermostat,flushed the radiator,chilton manual helpful,if you dont want to spend 16$ go to advance and they will let you look at one(chap.3-1)