Drive/Overdrive problems?

[joker1177]

2000 7.3 automatic with 270k miles. I just had my trannie rebuilt 2k miles ago after broken input shaft. New clutches, shift kit, input shaft and torque converter. It shifts fine and feels great but when im in 4th and start going up a hill at about 50mph it will do quick shifts back and forth from 4th to 3rd to 4th to 3rd(hard shifts in a 5 second time period) and then stay in 3rd until i get to top of hill then shift back to 4th. It will do it with cruise control on or off. I can also make it do it when i accelerate very slowly but only does it in 3 and 4 gears. the guy i had build it blames it on my P1211, P0470, and P4780 codes. I looked them up and they should have nothing to do with the shifting. Please help! Thanks.