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‘79 J10, rebuilt 360 & th400.
Downshift question...
Accelerating from a stop it shifts great at moderate acceleration and at WOT (w/ detent triggered).
When moving it downshifts appropriately when the detent is triggered either 3-2 or 2-1, and upshifts properly from 1-2.
When it downshifts from 3-2 due to detent trigger it doesn’t upshift back to 3rd as rpms climb and it struggles around at high rpms. Is there something to check or set for this? It works so well from a stop when detent is triggered so it seems odd that it would operate differently when detent caused it to first downshift.
I don't know a lot about transmissions, but i did fumble my way through a rebuild of my TH400 recently. the best advice i could give would be check all your vacuum lines and then your vacuum modulator. These are the easiest and cheapest things to replace but can really screw up your shifting as I found out.