Starter problems of the 2004 Chevrolet Tahoe

On an exit ramp getting ready to merge with traffic and the engine cuts off. I was able to stop. Turned the key repeatedly, and though the radio and dash lights came on the engine would not turn over. I had the Tahoe in "park" my foot on the brake. Nothing. Shifted it to neutral and tried: nothing. Movd the column up and down: nothing. Pounded on the column: amen it started. Drove to mechanic: could not duplicate problem. No data in computer indicating any problem. 6 weeks go by and Tahoe will not start in my driveway. Go though the same litany again. Finally started. My wife takes my Tahoe to lowe's in January car will not start. She tried so many times she drained the battery. I hooked up the jumper cables and it started immediately. I take it to mechanic and he "thinks" it's part of the ignition module, but doesn't know for sure. The part alone is $250. I decline to spend money on a maybe. Then for 4 months no problems. May 31st 2015, Tahoe will not start. It started fine may 29th. Not only would it not start, but the battery was dead. Radio was out of sequence by 8 hours. Charged the battery and Tahoe still would not start. Had a friend who is a mechanic come over to look at it and here's the part the really ticks me off. I get in and without any fuss the darn thing started, turned it off and it started, did this 20 times, it started every time. I would conclude that it was the starter, except for the fact that two times it shut off while I was driving it. We own three Tahoe's. 2002, 2003, and 2004. I don't have this problem with the 2002, and 2003 Tahoe's. Is this an ignition problem other's have experienced. Does it have any connection to the other Chevrolet ignition problems. I have two young son's and will not drive this Tahoe, with them in it.