Rear gear ratio question

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I am considering a different gear ratio for my truck. Currently has 3.73:1. Playing with an online calculator, I could go down to 4.56:1 and still be able to get to 135 mph in 3rd. My fastest trap was about 118 mph, and I can only add so much more power with my current setup, that I do not see me hitting 135 mph in the quarter.

So is there a reason not to go with the lower gear ratio? It should make the truck faster, correct? The only down side I can think of is traction,but their are ways to overcome that.