My grandpa has a 2006 Impala 3.5 with just over 9,000 miles.

I noticed that the exhaust smells really rich and the exhaust note is slightly different than when new.

Unless I drive it, it's driven very slow (the engine usually staying under 2200 rpm) and it's idled a lot. Could it be that the catalytic converter is clogged by such slow driving?

Last, the transmission doesn't like to shift at high rpm like it did when new. What are different ways of reprogramming the tranny from my grandpa's slow habits to shift well when I drive it? Any help with these two problems is appreciated.

Some fuels can cause different odors in the exhaust particularly sulphur, if anything was out of whack enough to make it run rich you'd have a check engine lite. The pcm has adaptive capabilities to control trans shifts based on the drivers habits.

The exhaust odor could indicate a failed CAT. The shift issues also could be the sign of an exhaust restriction caused by CAT failure.

The car is so new that you should visit the dealer and have them diagnose the CATs specifically -- it's a free warrany repair if the CAT is dead. A good dealer should recognize the issue immediately by performing an exhaust back pressure test, or by noticing the odor.

There are several threads on this issue -- but your's is probably the first for such a "late" model Impala -- symptoms are symptoms, so get it checked out.

Thanks for the advice. I think I'll take it down to the dealer and see what they say. I'll post back with the results.

By the way, can the pcm be easily reset so it can "relearn" driving habits?

Yes, disconnect the battery for a few minutes. But it will relearn with a new driver after a period of driving, do not do this before taking it in.

I took it to the dealer last friday. They said that they didn't find anything wrong, but they reset the pcm and gave it upgraded software. Thankfully, that fixed all of the problems. They did it all for free (warranty) too. The exhaust smell is normal now and the transmission shifts amazingly smooth at all rpm ranges. Turns out that my grandpa's slow driving really did cause the pcm to adapt in a weird way.