[puppeteer]

When was the last time you had the filter changed in the trans? and or the fluid? The Clunk could be the locking paw if you were parked on a hill at all or if there was drive line pressure from the curb or something like that if parked against the curb. Or could be a U joint.

 

[puppeteer]

If you wait and it is something, then it could cause more damage to the trans. Which would increase the cost of the rebuild. They should be able to save mostly everything and just replace the clutch packing's. Im wondering if it isnt just a delayed shift from a bad valve or solenoid. Which would be much cheaper than a rebuild. Did you do the change at 70k or did you pay to have it done? Just wondering if you had seen alot of material in the pan or metal shavings on the internal magnet if you had done it. If yes then i would say its time for a build.