ok so if im not mistaken the lo3 with t5 came with 3.08 rear gears and i have a 9 bolt rear end to put in it wit 2.77 and i was just wondering if the gear change would effect the speedomiter and what the speedomiter change would be if i got 3.77 rear gears for the rear end ?

 

Yes your speedometer would no longer read right, but wouldn't be REAL far off.

Best way to find out is to find one of those highway roadside trailers the cops set up to show people the speed they are going. Or to find an officer to radar you as your driving by, turn around (safely) and come back to find out what is reading was. Granted, it won't tell you how far off it is by a % to determine the gauges accuracy at all speeds, but maybe do it at 2 speeds, like 20 & 60, then you'd get an idea of its accuracy over a wider range.