speedometer odometer calibration '92 s100 blazer

I finally got the truck running right and put larger tires on it. 245/70R16 . My question is, now that I have these tires on it I know that the speedometer is off by a few miles an hour, not to mention the odometer,
the anti lock brakes, shift points? etc. Should I be taking it in to a transmission shop for calibration, or is one of those $80.00 little gizmos that I see advertized a viable alternative? I'm going to be driving from New Jersey to Florida this summer and I have enough problems without having to pay speeding fines while out of my home state.
Thanks in Advance,
N.M.W.B.A.o.O.
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You will need to modify your DRAC. Here is a link that will help.
http://webpages.acs.ttu.edu/chdarby/DRAC.htm
Rita
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i can't imagine your spedo is off that much. i put 285/75/16 on mine and the spedo was off MAYBE 1.5 MPH. vato zone has started running parking lot diagnostics and they may be able to remedy that issue but again, i don't think its anything to worry about. have someone pace you to see if making any adjustments is worth the investment.
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