2018 Mustang GT T56 Magnum Swap

I'm having an issue after swapping a T56 Magnum transmission in a 2018 Mustang GT. The issue is only in third gear at part throttle the spark source changes to "Torque Control" and timing drops drastically (all other gears seem fine). I've updated the tune with the correct gear ratios for the T56 and well as made sure the min /max ratios had room either side of the correct ratio. This is on a stock whipple tune with the only other adjustments being for ID1050x and return fuel system. Any ideas or is the software missing something?

I did the same swap a month ago on my 2018 GT PP1 with Whipple Stage 2. The only difference is my tune has been highly modified from the stock Whipple tune. I haven't noticed any issues with a change in engine performance so I haven't bothered to log anything since the swap.

I made the same transmission changes to my tune as you did. For the min/max ratios I calculated the percentage offset between the existing min/max values and the MT82 gear ratios and used that to calculate the min/max for the Magnum gear ratios.

For the VSS connection I used the Bowler all in one wiring harness with reverse lockout. The Bowler instructions say to program the input to 12 pulses to match the Magnum and the output to 36 pulses to match the output of the MT82, but I noticed in HPtuners that both stock and Whipple tunes have the VSS P/Rev - Trans (ECM 5001) set to 31 pulses. So I reprogrammed the Bowler harness to 12 pulses for both input and output and set the VSS pulses in HPtuners to 12 also.

I guess I'll be doing some 3rd gear part throttle logs tomorrow to make sure I don't have the same problem.

This car has the Bowler harness as well. I checked his settings and sure enough, it was set to 36. I changed it to 31 and the issue got worse. I also tried setthe the box to 12 and the tune to match with the same issue. Oddly 36 in the box and 31 in the tune seemed to work the best. I'm thinking he has an issue with the box or his wiring. I'll update tomorrow.

FYI, I logged several part throttle 3rd pulls (between 1.0 and 1.2 load). My timing is fine. Spark Source stays on Borderline and Torque source stays on Driver Demand.

As far as the VSS wiring goes, Bowler recommends running the ground wire straight back to the battery and getting the 12V power somewhere other than the wiring harness connection for the old VSS sensor. That being said, I decided not to use the reverse lockout solenoid (went with the Michigan Motorsports solenoid delete) and figured that without the power consumption of that solenoid I could use the existing wiring harness 12V and ground connections. I've had no issues wiring it this way.