Problem with heater....

[TCHRISD]

I have a 98 1500 V6....120K. It has had an issue with the heater since I bought it over a year ago. It would not reach normal running temperatures and heater would not get hot. I have recently replaced the thermostat (195°). Which helped get it closer to reg temps, but still not there (between 150-170).
Is this a heater core issue?

Any help is appreciated........

[Chris Stewart]

Most likely.
If any stop leak has been used, it'll collect on the heater core also because of the slow water flow going through it.
I have a similar problem with my Olds Bravada and if it warms up tomorrow, I'll flush mine with the garden hose.
I'll take both heater hoses loose from the engine, slowly apply pressure to one heater hose with the garden hose, flush until it becomes clear then swap to the other heater hose and repeat.
I won't connect the garden hose to the heater hose with any clamp, just slowly put them together so's not to apply too much pressure. Most home water pressure can easily burst the heater core, go slow with a weak stream.