I've got an 03 suburban Z71 with 164,000 miles on it. I live in upstate NY, so when it gets cold out....usually from october to april...the tranny doesn't want to shift into overdrive. it usually takes about 10 miles or so before its warmed up enough so it will shift. is this normal that it should take so long. it shifts into overdrive just fine the rest of the year..and it always shifts fine into the other gears no matter what the outside air temp