98M427

I just got my car back after upgrading to a new 427 and had LS1 edit tuning on my PCM. While breaking in the new clutch, I surged the throttle and clutch inadvertently causing a couple of codes to set. P0141 and C1255. Now the engine wasn't fully warmed up so that might explain the P0141 code and I may have lost some traction causing some wheel spin momentarily. I don't know if the C1255 code should have been set. However, later the next day, I refueled using 91 octane vs original 93 octane fuel and drove across town to a car show. On the way back, I checked out the cruise control. It would not engage. It would display a set ##MPH message then 1-3 secs later it display DISENGAGE CRUISE message. This occurred while driving in 6th gear at various speeds above 50. I later tested 5th and 4th gears. It works fine in 5th gear but 4th gear is the same as 6th. Does anyone know if this is related to my PCM tuning or is my TCS system malfunctioning?