Well soon anyway. I didn't have heat in my truck at all really last year. More like semi warm air that was worse to turn on than anything. So I had my alt die on my today so I figured I would just replace my thermostat right away. Seems its not the thermostat. Felt the lines and the return line is cool compared to the supply line. Should I just try a flush before I decide to replace the heater core? I did one on my s10 and I won't do another one. I'd rather just pay someone to do it.