It could be the problem I had, the 4th gear pressure switch was not working. Most aftermarket chips will not lock the converter unless you are in 4th gear (OD). Your trans will shift into OD still with a bad pressure switch but the computer will think it's still in 3rd gear and not lock the converter. If you have a Direct Scan or Powerlogger I know those two will tell you if the computer knows it's in 4th.