Starter problems of the 2003 GMC Envoy

I purchased my Envoy new with 243 miles & have been the sole owner. My security light goes on & off intermittently & the vehicle won't start for 10-20 minute time periods. There is no apparent pattern w/when this will occur. I have been stranded in areas that I do not feel safe, oftentimes with my young children in the vehicle. I initially took the vehicle to albert GMC, where I purchased it (no longer in service, so exact date/mileage unknown). Diagnostics returned multiple codes, all related to the security system. They recommended that I have the remote starter removed that was professionally installed 11/2008. R&r car audio removed the remote starter & ran all of the wiring to assure it was sound. I next went to automotive specialists. Service history: 11/9/ran multiple diagnostics, unable to determine problem or replicate. 1/19/replaced ignition lock cylinder & case, at my insistence, based on online forums. 3/11/ran multiple diagnostics, unable to determine problem or replicate. 5/6/replaced ignition starter switch, at my insistence, based on online forums. 9/23/multiple diagnostics, unable to determine problem or replicate. 9/19/replaced ignition starter switch (again), at my insistence. 11/18/shop had vehicle for a week, attempting to get the problem to replicate, without luck. I have spent a good amount of $ and time/inconvenience in attempts to remedy the starting issue. At gm's direction 6 weeks ago, I took the Envoy back to a dealership,[xxx], & had to pay another diagnostic fee, which only showed that the passlock sensor was bad. I had the passlock sensor replaced 1/19/11 & experienced the starting issue again within 2 months. Gm would not guarantee their part since it was not installed by an authorized dealer, even though it was a gm certified part. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

Upon starting the vehicle and taking off the gear shifted, and then dropped down to the correct gear it should have be in. Transmission was replaced within the first six months. Also, starter made a clicking noise several times before starting. Then the vehicle shut down.