No heat when going fast

Could be a bad thermostat and clogged-up heater core or a blend door/mode.

[quote:9552b173fe="jordan_leslie"]I have a 96 Sunfire.
In the summer my car is fine and in the winter it heats up great and blows hot air if I'm driving under 35k...as soon as I hit the highway and speed up, I lose all my heat and it only blows freezing cold air.
It has a bra but I've even tried cardboard in front of the radiator and it does nothing.
I had the head gasket replaced 3 years ago and when it started doing this I brought it back in and they replaced the thermostat.....but still no heat.
Any ideas on what the problem could be? I would appreciate any suggestions, because I'm at a loss.[/quote:9552b173fe]


*****
I have a 97 with 182900 miles, 2.2 that overheated in April 04. I had the water pump replaced and have monitored that situation consistently. Now as of this fall, I have noticed that the heat registers barely above 100 especially if I am doing over 50. Even if I sit and idle, like in a drive thru, it doesn't get into the normal range. Am I looking at a huge expense to fix this problem? I am a single mom on a microscopic budget. Also, my A/C hasn't worked in years and won't hold a charge. Should I just get another used car at this point and can I find these parts in the junk yard? Thanks for any help you can give.
Elizabeth