Can't speak to the tire issue, but the way I went with my '05 Sixer is 3.73 gears, in anticipation of getting a ProCharger (supercharger) after my bonus next February. :eyepoppin From everything else I've read (on this site and other places), 4.10s would be the ones to get if you don't plan on a major power boost mod. (In fact, there are a few guys who went the 'Roid route, like Nitrous, and still went with the 4.10s.) The 3.73s upped the RPM/speedo/gear ratio by about 300 rpm -- in other words, I was running about 2300 rpm at 80 mph with stock gears, and now it's about 2600 rpm -- but overall am happy with the switch. My quarter times were not better afterwards, but that's mostly because I got only two runs that day and choked me brains out on both of them.
The gears themselves are pretty reasonable (200 clams or so, depending on where you buy them from)...it's the labor that will cost you the bucks, unless you've got car mech skills and do it yerself.
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