Air bubble ?

I replaced head gaskets on my 95' 3.0 v6 . Also replaced radiator, thermo and all hoses. All working well but now, I have no heat, and a/t takes long time to shift into overdrive. Maybe thermo not working correctly ?

Did you install a 180 degree thermostat? Jiggle valve up?

Try running the engine on a hill with the engine uphill and the heater operating. This may burp any air in the system. Turn on the rear seat heater if you have one.

Check the operating temperature of the thermostat in hot water.

Make sure the heater valve is opening.

You may have an air pocket blocking coolant flow to the heater core.
Try burping it as Brian suggested.

A garden hose and a little water pressure can force the air pockets out.

A prestone flush kit works best.

When I replaced the radiator & thermo, I flushed it . I will do the hill trick as soon as I can. I didn't know I had to turn the rear seat heater to full hot with the front seat when burping. See, I live in Arizona, and its been between 100 and 116 degrees out. I use the air while driving in town and on highway. The clutch fan seems to engage fairly quickly and stay on while using air. Is this normal ? I don't get overflow boiling and overdrive works fine, but at night, OD takes awhile to work. Temp guage is just under halfway even with the air, but before I did head repair, it overheated on highway and the temp guage was reading ok til' I pulled over and shut off air, then while idling went up. So I am alittle nervous that its getting hot with guage giving a false read. What are some things air bubbles could effect besides no heat, and overdrive ?

Depends on where the bubble is located, could affect the heat and OD coming ON, if it's near the temp sensor it could confuse the EFI ECM making it think the engine is cold when it isn't, making it run rich ...

Zero heat coming from the vents leads me to believe that the vacuum hose that goes onto the valve that allows heated fluid to pass thru the heater core is disconnected. You posted that you replaced the head gaskets........lot's of stuff to disconnect. This disconnected hose would cause the radiator fluid to NOT pass thru the heater core...thus...no heat. Could also be the reason for a late shift into O/D Vacuum leak=longer shifts at low rpm's when the engine should be pulling the most vacuum.

I guess I should of said it had heat after I did heads, but very shortly. I am going to be working on it next weekend. I will check thermo, might have been faulty from store. I also just last week failed emissions test.(carbon monoxide and oxides of nitrogen) where too high. Any ideas ?