Rebuilt pump is $245 ouch, but maybe it is time. I don't see how you could have hurt anything by driving it in third at 70. I don't have to shift to forth on mine until 80 give or take, the SDL probably would only be turning in the low 4k rpm range at 70 in third. When was the last time your power steering fluid and filter was changed?

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200