HitmanX posted up some good info on this.
Diagnostic Information on Diagnostic Trouble Code (DTC) P0894 and P1870 - Team ZR-1 Corvette Racers
Seems like the converter is slipping. Either way the trans has to come out again.... I'm taking the truck back to stock to sell it anyway, I just wanna make sure the trans is ok before I sell it. If the converters bad oh well. Probably send the trans to chuck to go through.