My 92 5.0L takes forever to warm up in this 20 degree weather. I start my truck and let it idle for a good 5-7 minutes and it's still pouring exhaust out the pipe like a smokestack and the needle is just barely starting to creep to warm. On the flipside, my gf's Blazer warms up in 2-3 minutes. I just replaced the WP, thermo and new coolant about a month ago so there should be no issues. I originally thought the thermo was stuck open but it wasn't and I replaced it while it was out.