I have a 1999 Ford f350 Dually 7.3L the other night I was driving it for 3 hours no hard shifts no slips. Backed it up to hook the boat up to it and then put in drive and nothing. have to floor it to get it to creep. Shut it off for the night and in morning got in it and it took off like normal but I notice it slipped little and now the od is flashing. Is this a sign of needing new transmission or is the solenoid going bad? Any ideas are highly appreciated. Just trying to get some insight before I dump a new tranny in it.