You should have posted in C5 TECH. You would have gotten a LOT more help quicker.
Anyway... In short,,,YES,,,the same size tires all the way around can and will cause TCS issues. Until you rectify that issue, its real tough to point you down other paths.
You also seem to have wheel speed sensor issues. Heres a FACT. From 97-2009,,,,,
,,,I have N E V E R seen a wheel speed sensor go bad. PERIOD. I have see wheel bearing assy's go bad (yes they are two separate assemblies. I have also seen sensor pig tail damage due to carelessness or an accident. The sensor part of the wheel bearing is just about bullet proof.
On another note, the wheel sensor wiring harnesses have female connectors that just plain SUCK. 90% of the problems that I see with WSS is due to female pin damage.
Heres an example of a good and BAD female pin The one on the LEFT is brand new:
The FRONT sensors use a jumper cable to connect the WSS to the main body connector:
The female pins in the female connectors go bad a LOT.
Anywhere theres a female pin,,,its susceptible and must be checked. I use a spare male pin to insert into the female pin and that tells me if the female pin has the correct grip on the male pin (sounds sexual doesn't:smilelol: )
Heres an example of the male pin:
I will say this. The Reduced Power problem has NOTHING to do with EBTCM or tire sizes. It involves the Throttle By Wire system. DTC 1281 (APP Sensor 2 Circuit ) caused that problem. Check the accelerator position sensor connector and wiring. If the problem persist, remove the sensor and read it with an ohm meter and make sure that the resistance reading is smooth and linear thru out the range of the peddle. The are Three sensors in one sensor One reads high going low and the other reads the opposite. The other does something else:
Something else to note: 97 and early 98 C5 had issues with the Throttle Actuation Control (TAC) module reliability. It was detailed in a service bulletin. The recommended fix if the car had specific problems causing it to go into reduced power (displaying specific DTCs) was to replace the TAC with a 99 or newer TAC module. I had a early 98 and had to replace the TAC module ($250)
You seem to have an issue with APP circuit 2 so, I would concentrate there first. Check that sensor.
BC