Chevrolet Repair: engine runs cold, upper radiator hose, degree thermostat

Question
Hi Van, hope you can help. Got an "86 S-15 Jimmy, about 12K miles on rebuilt engine (2.8), only warms up to about 145 degrees as per a thermometer in the radiator and the temp gauge - cold weather or warm doesn't make a difference.  Put in new 190 degree thermostat, found it had a 195 in it. Tested them both in hot water with thermometer, both work. Tried blocking off heater hose - an auto forem thread on same subject suggested there should be a restrictor there, didn't make a difference. Has an HD radiator, installed with engine rebuild. Seems to be tuned properly, but it's even more gutless (and poor mileage) than it used to be - running open loop?
Thanks, any suggestion will be appreciated -
Russ

Answer
Hi Russ,
Sorry this is so late...I was out of town taking care of some parent plans.
Now if you are checking it with the thermometer in the filler neck of the radiator, then the coolant has already passed through the heavy duty radiator, and it may well be more efficient than you want.
But where the coolant needs to be checked is where it comes out of the upper radiator hose, which is the thermostat released coolant.
You may have a bad temp sensor, giving the ecm a false reading, thus staying in open loop.
And if it is running too cool, why did you replace the 195 with a 190?  Gonna open sooner, at a lower temp.
Van