90 Jeep Heat problem

1990 Jeep Cherokee 4.0L has very little to no heat. So far the thermostat has been changed twice, it has a new radiator (leak) and a new fan clutch. Mechanic now wants to throw in a new heater core.The temp gauge does not go up past the 130 to 140 mark but all hoses including those into the heater core feel much hotter. Mechanic put cardboard infront of radiator and after running the electric fan kicked on. It also looks like its not moving a lot of antifreeze into the pressure tank. I believe it still has the original water pump and its at 113,000 miles.... Im stuck, is the temp sensor bad, or water pump or both. Any suggestions ??????

its possible its the water pump but before you spend the money pull the upper rad hose off and manually pour water or coolant into it until it spills out the thermostat housing alot of the time those 4.0 motors become airbound after service which will cause little to no heat and sometimes overheating.