I live in Minnesota where it has been very cold lately, and my truck has had issues when I put it into reverse. I will let the truck warm up for a few minutes, but when I put it into reverse it does not start moving. I will have to rev the engine to around 2000 RPM's before it will go. I have had the truck for a couple years and it has never done this before. It is an 04 Silverado Z71 with 160K miles. It does this even on days when it isn't super cold (above zero). Any ideas? I was thinking of just changing the transmission fluid to start with.