2001 blazer 4lo flashing by itself?

Just started yesterday it will flash for like 10-15 seconds and stop for less than a minute then do it again.If I put it in drive while flashing it goes into 4lo so I have to wait for it to stop.It also continues doing the same thing while driving?I have read through other threads and none seem to be the same as this.Maybe I just didn't see it but I could really use some info please.