right when the real cold of winter flares up, my truck decides it doesn't need to keep me warm anymore. Basically it started the other day with ...stays cold after about 20 minutes of run time, then gets sorta warm...well tonight I ran it 50 minutes on the interstate and I could still see my breath in front of me as i got to the house..my toes are numb.

I noticed that the factory temp gauge would go from Cold...slowly crawl to Hot, then instantly drop down to a mid range level...seems to do it nearly everytime.

I checked the heater hoses after shutting it off..they are only warm from the engine heat...the top radiator hose is fairly warm..the bottom one is warm from the engine heat..nothing feels toasty hot.

Any input? 150,000 miles, i replaces pump about a year and a half ago.