Unleashed beast,
I think the lower thermostat could have been a contributing factor to the sludge. Especially considering you were making short trips. Your oil just wasn't getting warm enough to burn off condensation, etc. If it was my car, I'd stick to the OEM thermostat, and then possibly play with the fan speed/cycling only if needed to prevent overheating.
Noticed where you are at, and I'm only about 60 miles west (towards Shreveport) of you. I'm at exit 44 of I-20.
Anyways, with that low thermostat, I wouldn't doubt you'd get lower fuel economy, especially in winter. Depending on how GM has your car programmed, you may have been running in closed loop mode all the time in the winter, which would really exaggerate your problem.
I'm wondering why you would need to get your fans on earlier. If you advanced the timing, or leaned out your mixture a lot, then I'd start becoming concerned with heat (but in your case, you were probably ruunning rich). I actually ran my old '96 Maxima here in the summer with only one fan operating for a month before I could replace it. The Nissan tech told me it was safe, and it didn't hurt anything. The only problem was my AC was hot whenever I stopped at lights. Of course my temp gauge is one of the dumbed down ones (no numbers, it just goes to the middle for its normal range), so I couldn't even tell my coolant temp differences. And my commute was 35 miles of almost all interstate to Shreveport. If LS1's don't have an inherent overheating issue, I'd probably just monitor the temp, and if in specs, leave the cooling system pretty much stock. Just watch for pinging under load in our blast-furnace type summer heat!
I've been thinking of using Auto-RX in my '97 Maxima mainly just because it has 104,000 on it, and I believe in preventative maintenance. And Auto-RX has gotten some really good reviews. Actually, I don't think I've read anyone say it was bad. Let me know how it does for you.
Have you taken that car to the strip yet? Red River Raceway is just north of Shreveport. I've thought of going just to check it out (and running my car just for laughs).
I'm having a little carbon issue, along with Sky Jumper in his '99 Maxima, in this thread:
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=003935. Looks like we both do relatively short trips, too (I no longer commute to Shreveport). I'm probably going to Sea Foam mine tomorrow (vacuum line) to try to get the pistons shiny again.
Keep us up to date on your Auto-RX rinse.
Dave