Speedo recalibration possible?

I swapped the rearends out of a 92 sierra 5.7, 5spd stick with a 3.08 ring and pinion, and a 93 sierra 4.3, 5 spd stick with a 3.43 ring and pinion. Now the speedo's are off a bit, one reads high and the other is low. I can't believe the lack of info on how to get the speedo recalibated. Local dealers can't do it and don't know where to send me to have it done. The transmissiions both have elecronic sensors/counters on them and therefore can't be adjusted the way the old style cable drives used to using a swappable nylon drive gear. I'm told the cluster has to be re programmed but the dealers only have the ability to flash the original factory data from the serial number build info back into it. I see a recalibration device is available thru Summit Racing but the $300 price tag is not cost effective. Someone has to be able to reprogram this thing! People are looking at me like I've got 3 heads for doing what I did, as if they'd never heard of doing this! Help!