Ford Repair: Ford F150 starting problem, engine cranks, private shops

Question
Hi, I have a 2003 F150 and have been having starting problems for the last 1 1/2 years. It has been at numerous Ford dealers and private shops and nobody can fix it once and for all.it's hit or miss with starting. So far the computer, sensor ring on ignition switch, some sort of power relay(that controls the computer)have been replaced works good for a bit and then same thing. Engine cranks anti theft light flashing but wont start. odometer flatlines. I had a remote starter installed prior to this problem and still think that it may have something to do with it. At 1 point I went back to them and had it disconnected, but problem still rears its ugly head from time to time. It was ok for the past 2 months  after the chip sensor ring was replaced so I had the remote hooked back up with winter here now. and have been having trouble the past 2 days same problem anti theft light flashing, cranking but no start.PLEASE HELP ME I don't know what to do anymore, and the dealers keep telling me there is nothing wrong they cant get a code other than the anti theft was engaged and the truck wouldn't start but it won't say why. I know it's not the battery, starter, fuel pump. The problem lies somewhere in the anti theft. Thank You Jim

Answer
the antitheft is the cause you are correct but what is triggering it may be hard to find-the theft module or cluster would be where i checked first if you didn't have a remote start system installed those things can really throw a wrench in diagnosis even though you had it disconnected at one point but unless i misunderstand since you've had it reconnected it has gotten more frequent-i would have it disconnected until the problem is definitly found. intermittents can be a bear to find but if it worked ok after ring replaced until remote reconnected then undo it. check iac motor for sticking cold for crank no start i don't think that is it but you can't rule out the possibility of having two seperate problems.sorry i can't be of more help