93 s10 blazer lack of heat new parts installed

i have a 1993 s 10 blazer with the vortec motor.  I resently replaced the heater core cause it was leaking.  Well now it's and my motor isn't getting up to temp.  I have replace the thermo stat and a new pressure cap.  With no luck, I installed a temp gauge cause the dash one wasn't working.  When driving down the road it's reading 170 then goes up to 180 and back down to 170. 
 
I am thinking of a possible fan clutch that is stuck on.  Is there a good way to test a fan clutch.  LOL the guy at the auto parts store said to grab a hold of it while it's running (which I said sounds like it's hard on the fingers).

r u sure ur thermostat isn't stuck open even tho u just replaced it?

sounds like u installed a 180 degree thermostate i wouldn't worry if its running that temp and everything operated ok

I was going to go buy a GOOD thermostate and replace it.  It use to run for 15 mins and blow good hot air.  and the mileage is crap now with it. 

then get factory oem thermostate and install and b sure to bleed coolant system good when filling back up with coolant should solve problem