Very little heat. Coolant sensor reads in cold range most of time. Seemed like t-stat stuck open. Replaced t-stat. Same problem. Any suggestions?

Your coolant circulation could be plugged up... might want to drain it and flush it out. Hook a hose up to it and check the flow. The reading on the gauge could also be due to a bad temp sensor... but since you are not getting heat from the ehater it likely is not the case. Seems you have a circulation problem. Be sure the thermostat was the correct one and that it was isntalled with the copper side toward the block.

start the car get it warm and take off the radiator cap and see if the fluid is flowing if not then its pluged or you got a defective thermostat