I have an 02 silverado . Originally had 0411, 4.8 4l60e. Over the last year I have been changing, upgrading parts to my liking. I have now a 6.0/4l80e with p59. My motor was replaced first, then the transmission and recently the ecm. My transmission had been working very good until I put in the p59. The p59 ecm came with the transmission 4l80e, along with an 4.8 engine and harness. I assumed I could install the p59 and not have to touch the trans settings and be fine. The trans acts seems like it doesn?t want to shift but slowly goes ahead and does. I put it into reverse and it seemed to not do anything. I didn?t give it much throttle for fear of tearing something up. Is there anything that needs to be done to the harness in the truck to run an 05 p59. I have already performed the 60e to 80e wiring change that I found on lt1swap. Now that I?m running the 4l80e and p59 through a 0411 harness and earlier year I?m wondering if some wires need to be changed or added. I hate to think there?s something mechanically wrong with the trans. I?ll look into that possibility, but also want to make sure the trans is getting the correct signals from the ecm. My trans issues started within the weekend of installing the p59.