Cadillac Repair: cold start problems, cadillac fleetwood, temperature gage

Question
1986 Cadillac Fleetwood Broughm with 5.0 liter with carb.  

I have had problems with no heat in the car for a few months.  Changed the Thermostat and rechecked twice,New Radiator,Checked water valve, cleanded EGR (pinging).  Now, the car dies when cold and under load,it seems to be running fine and then it stumbles and dies. It will not start for an hour.  IF allowed to warm up for 20min. there are no problems.  The car does not seem to be getting up to temperature it takes 40  minutes of driving for the heat to finally come on.  What can be wrong?  Any suggestions to get car more drivable?  IT is like brand, and I inherited it from a family member.  I would like to drive it, but it is just not reliable enough and has already cost me several hundered dollars in tows.

Answer
Is the engine temperature according to the temperature gage warming up as it normally does ?.

Your problem is that it is just that you are NOT getting any heat thru the vents for the inside of the vehicle ?.

Is or does the check engine light come ON on the dash ?.

What mechanical work of anykind has been performed on the vehicle ?.

autohelp