Low engine temp/no heat on 2000 Chev

I have a 2000 Chev S10 and the engine temp never seems to rise above 100 degrees. I've change the thermostat twice. I also get no heat. Besides checking the heater control valve is there something else to look for or check?
1st thing you probably want to do is make sure the gauge sending unit is accurate. Either compare reading with the comp temp sender on a data stream or measure the engine temp with temp gun or other temp measuring devise.

As far as the core goes, check to see if both heater hoses are getting hot............
?? Running that cold! Is T-stat in right position? Some can go in backwards - no many but should be on the list. Spring end goes towards engine of typical thermostats. Does upper heater hose warm up quickly? I should end up about to hot to touch but stay stone cold till thermostat opens if not the thermostat still isn't right!
 

I meant to say it runs about 150, it normally runs about 200 degrees. The thermostat in in right because it wouldnt fit backwards. The 2 hoses heat up. I even ran the engine with out the radiator cap and can see the water circulating. The only thing I noticed was the 2 hoses that go into the firewall are cold.
Sounds like it may be plugged up with Dexcool sludge. I would put some flush chemical in and then flush it thoroughly with a garden hose.