I had the same thing happen last summer - 3 times in one week. Like you, I cleaned the ECM plug and fuses and added a little dielectric grease. I also cleaned and greased the plugs on the back of the speedometer and tach. It has not done it since. You might give that a try.
2005 FLTRI Black Cherry, 95" Big Bore, Thundermax w/Auto Tune, V&H Dresser Duals w/Klock Werks SS, Andrews 26 Cams, SE Stage 1 intake, SE OD/6 Speed, Wards FCS cooling fans, Krome Werks Stretch Heritage +2 bars, Progressive Monotubes, 444's, & Touring Link, Michelin Commander II's, 14.5" Madstad, Lowers with Classic Motorcycle Vents, detachable King Tour Pack, Daymakers