Turbo 400 mated to a new (about 1500 miles) mildly built 400ci small block in an 86 c20.
When cold it shifts fine, as it comes up to temp the shift point goes from it's typical shifting pattern to shifting at about 3500 RPM. There is no engine breaking like there would be if I were manually shifting, or what I would expect if it were just stuck in gear.
I replaced the modulator and inspected the vacuum line. Line is good and new modulator did not make any difference. Fluid levels are good. I did find that one of the lines leading to the trans cooler was very slightly kinked, probably happened during or shortly after the new motor was put in. I straightened it back out and it should be flowing well. The electronic kickdown is not working (that was next on the list to sort out) and I have not yet trouble shot what is going on there.
Any idea what is going on?
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