Originally Posted by
Russ K
Just solved the same issue with a 1976 Sierra with a 5.3/4L60E with the OEM manual transfer case. Had a speed signal generator inline with the speedo cable. First got the scanner speed to match a gps, this is done with the "VSS Pulses Per Distance". Next log the output shaft RPM while driving. To calculate the trans mile per hour, do this; (trans output shaft rpm*60)/trans output revs per mile (which is 2,230.1949 in your tune)
So you need to get the trans mile per hour to match the vehicle speed in the scanner, if the trans mile per hour is low, lower the "Trans revs/mile" by the % error of the vehicle speed in the scanner.
Also look at you shift speed tables, your 1-2 is at 141 mph. What I did on the 1976 Sierra was to start with a stock tune, and change the tire size & gear ratio to what the truck has currently. Then copied all the shift speed & TCC tables to the modified tune.
Russ Kemp