1999 Ford F350 no 2-3 shift

Hi, I have an 1999 f-350 superduty 7.3ltr diesel.I just serviced the transmision at 140,000mls, along with all the oter fluids. Today while I was out the trans shifted into 3rd harsh once, about 10 mls down the road it seemed to lose 3rd completely.I pulled over and checked the fluid(pink and no smell), I run a flashpaq tuner so I checked it for codes and it came up with po733 3rd gear ratio error, and po782 2-3 shift error.I cleared the codes and and put the flashpaq tuner back in stock mode and limped to my destination (a couple of miles). On my way home that night (a couple of hours later )the truck seemed to shift fine for about 1/2 an hour the it started to lose 3rd again(but the overdrive still works).I limped the truck home and checked the codes again and it had the same codes again allong with po782 internal ctrl mo kam error). The manual I have is useles for transmisions.I'm hoping there might be a bad solonoid, or something. Thanks for your help Chris