[shorod]

I'd certainly suggest you start with the diagnostic codes before spending any money on the transmission. You'll probably find fixing the codes "fixes" the transmission as well. The P0171 and P0174 are very well-known codes for the V6 LS. There's an 11-page thread about them so I won't go in to the detail here. You can either check the LS forum thread listing or use the "Search this forum" feature.

The P0430 code indicates that the Catalyst System Efficiency for bank 2 is below the threshold. I wouldn't worry about this code until you get a few of the others fixed, but you will want to address the others before you drive this car much longer or you will destroy the very expensive catalytic converters.

Code P1112 indicates that the Intake Air Temperature (IAT) sensor is intermittent. This is probably the issue that's causing what you are feeling as transmission slip and could very well be the source of the P0430 code. I'd start with this code.

Code P1565 isn't listed in the Powertrain section of the factory service manual for the 2002 model year. I'd have to do more digging which I don't have time for this morning. If someone else doesn't define that code before this evening I'll search some more.

-Rod