I'll have to say the lower temp thermostat won't do anything, for multiple reasons.
1. modern fuel injected engines are design to run warm (190-210)
2. less wear occurs in a warm motor
3. fuel economy will decrease with a cold motor, blah blah blah...
Everyone I've talked to (including GM engineers, FWIW) say to run at the minimum a 180^ thermostat. Any colder and the engine may have difficulty getting up to temperature, which is counterproductive. Warm is good. [img]/wwwthreads_images/icons/smile.gif[/img]
About the Hypertech...it's decent for gearing changes, but that's about it. I had a friend (who shall remain nameless) program my PCM with a Tech-2 *Flash*, and did a bunch of stuff...removed timing retard on WOT shifts, increased line pressure in trans @ critical points, changed the speedo, changed the timing curve (more agressive, but I can still get away with 89 octane unless I'm at the Dunes or something), eliminated torque management, and...removed my speed limiter. My truck's been over 100 mph on a few occasions now, and I can't decide if it was a good idea to remove it or not. [img]/wwwthreads_images/icons/cool.gif[/img] It does pull significantly harder in 2nd gear, so I'm happy.
BTW...I noticed a huge loss in performance from the 31's to 33's. Anybody who can't tell doesn't have a very sensitive butt-o-meter. I'm not sure, (haven't run it at the track yet with the taller tires) but I think after the PCM redeux it's still a little slower than stock. Milage got worse, too.