I just changed transmission 2months ago now I put it in gear it doesn't move at all but yesterday it ran fine.I check the 1974 Chevy truck c/10 . The only thing I see wrong was a empty brake fluid resevor
If it's an automatic, I would slide under the truck and check out the linkage. My old '85 Scottsdale had a bad linkage. Would pop out all the time because the bushing got worn.
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