my blower stays on when key is in off position can you tell me why this is

 

I have an 01 with the same problem. I noticed this when the temp was in the low 30s and 20s this year, most of the time I turn off my accessories before shutting the truck off but, I forgot to about 5 or 6 times when the weather was very cold and this was the result. I haven't been able to track down a solution to this and until now I thought it was just my truck, I have also noticed the blower slowing down momentarily when I come to a stop light and while I would think that the two are unrelated it is a little wierd that both involve the heater blower. Any help would be appreciated.

 

My 02 SCrew did the same and found that there was a small leak in the upper left(driverside) corner of windshield. Water accumulated on the GEM and fuse panel and caused the fan to constantly run and several other problems. Fixed winshield and dried out fuse panel, and everything works 4.0