About three months ago my 2001 silverado quit. I had it towed to the chev dealer. We both thought it was the starter. Had a new one put in, they called me to come and get it. Fired it up to leave, a bad sound. Left it, they called me back the next day. Found out the karr alarm I had installed many years ago when I bought it new had somehow caused the problem. They took it off and I have been good. The service manager even said that somehow it affected at what speeds the auto transmission would shift. I now notice a huge differance. There are large long climbs between where I live at cedar city and st george utah. I drive it once or twice a week. I use the cruise control and now see that the truck on the same stretchs will go much farther up a hill before it downshifts on the sane road. There are certain points on the freeway where I knew it always downshifted and now it either wont downshift at them or go much farther before it does. The way it was it would downshift from drive down to third but then soon downshift to 2nd and I would have to be quick to tap the brake as the engine would be screaming. Now that seldom happens. It was a add on car alarm and the brand was "karr alarm". I cant tell you how or why it can affect the transmission technally speaking doesnt make sense to me either, but the service tech said it did, and I can tell it did! I also own a 2,000 gmc sierra with the bigger engine. If I ever buy another truck I will get the bigger engine option. In my experiance the smaller engine gives little or no better gas mileage and has less noticable power big time in the mountains here. Both trucks are the extra cab short beds.