Unusual Transmission Shifting Issue
 

A friend of mine is having a problem with his truck. I invited him to join the forum.I'm hoping he shows up soon. but in the mean time I copied his facebook post


Hey guys I need info, My 03 silverado is acting up again, won't shift on it's own, it will manually shift, but sometimes when in drive or overdrive it will jump into second gear, and stays there until I manually downshift and bring it back up again. The fluid in the tranny is red. The abs, brake, and service engine light are on, the only code that shows is a missfire on all cylinders. I changed pretty much all sensors, ecm, and done a complete tune-up. The engine has full power and no missfire, but does idle real low sometimes almost to a stall. Any info is appriciated. Scrapping the truck is not an option! LOL! Thanks!

He mentions that the fluid is red, but is there enough fluid?

He says the fluid level is good and the fluid is new as well as the tranni filter.

Its an electrical issue. The harness for the ignition switch powers the trannys electricals. They build up resistance over time and eventually stop working. Try replacing this to see if it solves your problem. Autozone has it for bout $79. They told me if it didnt fix it, I could take it back. This article shows you how, not sure if it will apply to your '03, but it should.

How to Replace an Ignition Switch in a 2000 Silverado : How-To Articles