P0781 Code 1-2 shift problem

[DJM]

This is for my buddy with a V10 truck but he was towing a utility trailer over the pass this weekend he had it out of OD not much weight in the trailor just a little firewood tent chairs and coolers but he was heading up the grade and he said it would rev up real high before it would shift to 2nd gear. He could get it to shift fine if he let off the gas and it shifted so I hooked up the AE on it last night and it had the P0781 code and one for the input shaft sensor.deleted the codes we went for a drive and from 1st to 2nd it slips real bad checked codes again and it just had the P0781. Time for a rebuild? I checked the oil and it looked burnt but didn't smell like it He doesn't know the last time it was serviced so I told him to do a oil and filter change just to see if it changes anything. Can I check into it more with the AE to find a problem?

[HOUTX01X]

i think that was one of many mine was throwing too> had it rebuilt. my tranny was toast though smelled like burnt fluid and looked like it. od light would flash after a few minutes of driving.