Tranny Slipping and No Overdrive

[JMAC2354]

Posted this in tranny problems, with no advice, so here goes in this section. I have 2008 110K miles,4x4 intake exhaust egr delete, running H&S HD300 tune. I was towing trailer on interstate today, went to pass a car got on throttle pretty good, clunk clank studder etc, and finally went back in gear but would not go into overdrive, had wrench come up on display at this time. Drove on home at 55 to 60 mphs, turned it off let it cool down wrench disappeared, went to back trailer in drive noticeably slipping in reverse anyways, pulled tranny codes with H&S came back P2703 and P0766, which I believe are both solenoid codes. Anyways give me some ideas guys, gonna try to limp back to town tomorrow, would it be worth trying fluid and filter change, or is this tranny probly gone. If so what would be the best options moving forward. Truck is driven with tuner obviously but not tracked or raced, I do use it frequently towing 6-8K lb loads, and the occasional need to feel the power. Thanks for any advice.

[04hdfatboy]

You might want to replace the DD solenoid. Gogo diesel makes a direct drive solenoid that makes the 3-5 and reverse shift much firmer. It might help with your problem and is a good investment for the transmission.