4r100 od problems

[jonesn619]

I put a bank trans commander on about 4,000 miles ago, went camping in the sand, i had the od off and ever thing was good, the truck sat for a week or two, then drove in a rain storm, the od light started flashing, 1-3 gear work good but no od .I took it to a trans shop the code they came up with was 3rd 4th shift problem, but had no clue what it could be .I don't have $4500 to get a good trans, any one have an idea what it could be? the truck is an 2000 F350

[jonesn619]

I took the banks off, and still the same. It will go in od or I think its od, but not for long gos back to 3rd. Been driving it as a 3 speed, runs good, but no od, any one have this problem before, please help!