I have a 98 C1500 5.7L 4L60 transmission I am finally getting around to tuning the truck on a few things. Main thing I'm having issue with now is getting the speedo correct. I changed my gear ratio to 3.42 but no change still way off. I tried the speedo calibration wizard, and it caused my trans to act very weird, holding gears. I will add I do have the 120mph cluster in it but from my understanding its a direct swap, so im not getting something right in the speedo calibration tab I feel like.

Factory 3.08 235/75/15
currently 3.42 275/40/20