190/195 is the factory heat range. Coolant temp dropping by 10-15 degrees won't change heater operation much except in the dead winter where it will go from feeling very warm to moderately/luke warm. I'm talking 20 degrees and below.
If you had no heat prior to changing the thermostat then its not the thermostat, if you had heat before the thermostat, it may be the thermostat but its unlikely, crib deaths on anything other than bargain bin thermostats is pretty low.
Some things to try. Warm the truck up to operating temp by driving it or idling for 20 minutes. Feel the upper radiator hose, it should be pretty hot, just about 180 degrees. If not, rev the truck to a couple grand and see if it warms up. If it doesnt then feel the heater hose, it should be hot. If neither are hot then you're likely looking at a bad waterpump, to tell for sure feel the bypass hose which is behind the A/C compressor and between the intake and block, it should be hot.
If the rad hose is hot then you'll need to check the heater hoses. They should be firm not spongy, and both should be hot. One will be slightly hotter than the other. If one is hot and the other is cold, or both are cold/lukewarm then its highly probable that your heater core is plugged. Sometimes a borderline heater core can fail just by draining and refilling it. Don't bother trying to flush it, most of the time doing so, even gravity flushing, causes leaks and will just lead to replacement anyway, and coolant residue on your windows. That sucks to get off.