recently had to do a gear swap from 4.10 to 3.55. Why on earth would someone do this you ask? started getting some vibration from the 4.10's, and took it to the dealer to see what was up. told me the install job on the 4.10's was bad and that there was too much backlash and had worn the gear teeth. so i needed a new ring and pinion, only problem is that only a reinstall of factory 3.55's would be covered under warranty. Dealership had advised the warranty company that i had existing 3.55's, so that they wouldn't deny the claim. so now im back to 3.55's and of course there are some things that need to be changed. First, the speedo. and since my search for an existing speedcal or some other calibration device turned up nothing, my question now is, how can you tell if your car was tuned before? im assuming with the mods and lack of a speedcal or other device that it had been tuned somewhere before i bought it. Assuming the car had been tuned, in addition to the speedo being off, what would a reverse gear swap do the MPG assuming a previous tune exists? I lost 4 MPG going from 4.10 to 3.55 and that's bull*****. thanks guys...sorry for the long post.