The 700R4's mainline pressure is derived from TV Boost and the PR valve. If the TV cable is loose line pressure will be low. With low line pressure apply devices can be overcome by tractive load and the result is slipping. It doesn't take too much slipping to allow too much clearance within a clutch pack of a weak old 700R4 and the end result is a slipping burned clutch pack. If it doesn't feel like it's upshifting too fast and it's not upshifting too late then put a witness mark on it for a good baseline. If you want to play with it from there tighten up the cable one click and see how it goes from there. You can always go back to where you started by your witness mark.
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