Then you have a hose, radiator prob or thermostat prob. And yes, I forgot to say WP. I replaced mine a couple years ago and still had the WARM heat issue.

 

You have air trapped in heater core.Just did all this on my truck{same as yours but 99}.Feel both heater hoses going into core.If they arent both too hot to comfortably hold then you have trapped air.I fixed my truck with lisle cooling system funnel{napa has them}.My heat is money.

 

So I replaced the water pump and flushed the shole system out. Took off all the hoses to make sure they were in goo shape. The anitfireeze was very dirty. It cames clean after flushing and back flushing for a couple of hours.

I still have little heat. I had the front of the truck lifted in the air on the hoist to make sure the radiator was the highest point, which should do the same as that funnel tool, I am familiar with it.

So now thats a new water pump, antifreeze, thermostat, heater core and I've had the heater box out to make sure the doors all work right.

Any other ideas? I know the radiator flows good.

 

hmm. you've replaced the whole system.
where are you, down south or up north ?
are you using a 195* t-stat ?
did you drill a hole in it ?
where on the temp gauge does you needle sit ?

you may have to raise your engine temp some more. either with a hotter t-stat or block the radiator. does anyone list a 205-210 t-stat ?

 

I live in Northern Alberta and it does get very cold here. The truck has a 195* thermostat and it runs right at 195* on the temp gauge. I never drilled a hole in the thermostat.