I'm not entirely sure on what the problem is? Is there a group with stock/fixed gearing?@DolHaus Do you have any ideas or solutions? Seems to be that more than 1 car needs to be used for testing. With similar power upgrades on each different car? Would that not blur the results and keep tunes as they were intended?
Forgive me if that 1st part didn't sound right, just a question not a shot.
If its a case of the increased revs gained by power parts screwing up the stock gear ratios then I would suggest testing the cars that don't have any engine parameter changes first (Engine Tuning 1/2/3, ECU upgrade and Exhaust all change the rev limit). Maybe try resetting the trans once parts are applied/removed? I'm not sure what issue we're trying to solve here?