There is no speedo gear on the 4T60E. It uses a magnetic pick up with a reluctor ring set up for 24,000 PPM (Pulses Per Mile). No you can't get a reluctor ring cut witha different number of teeth. The ECM needs to be programmed for the actual PPM input. This can be done by the person who programmed your ECM. Hit me up if you don't have someone who did your programming.
4T60E VSS pick up
Not the 4T60E reluctor ring but a generic example
The 4.9 Caddy ECM uses a PROM chip, not flash programming. The plus on this is that you can 'reprogram' your ECM by swapping the chip. Flash programming would have required you to send the ECM to someone to have it programmed.
My emai if you don't have someone else to program the ECMl - email@example.com
[This message has been edited by phonedawgz (edited 05-21-2014).]