One problem related to gas recirculation valve (egr valve) has been reported for the 2003 Chevrolet Trailblazer. The most recently reported issues are listed below.
When it is cold outside and the engine is started it knocks and ticks until warmed up. Gm customer service will offer additional miles on the warranty but no additional time. The dealers will not fix the problem. Gm says it is a piston problem. This problem happens every day below 50 degrees. That is 8 months of the year in michigan. The truck is embarrassingly loud. Sounds like it is 20 years old. It is only 5 months old.