Thanks for the help in advance.
My 2000 7.3 has 230k miles and 30k (3 years) on a rebuilt trans. The past 3 months the O/D light comes on after a few miles and randomly the speedo stays at 0 until I stop and turn off then back on. I drove almost 1000 miles in the past 2 weeks and I noted it was shifting hard through all the gears. Today I let the truck idle for 10 minutes (AC for the dog) when I get back in and put it into gear there was nothing.. As if in neutral, I moved the shifter through the gears with different rpms.. I turned it off and sprayed electric cleaner into every plug that went into the trans and a cluster of plugs a over the drivers wheel well. It then engaged as normal and I drove a few miles until a stop then it slipped out of gear and didn't re engage. After the hour tow home it engaged as normal and I parked it. Now guys. Where do I start?!?!? Trans filter change? More electric parts cleaning? Valve pack?