A/T 4speed fails, car wont move until hot.

[fixkick]

the OD flashed 12s..?

as you know engine full power must be at hand, 95HP on tap.
if not, the transmission can't do much. but get confused. (trans measures speed and engine load to shift)

so full power in 1st and second.
then fails to shift in to 3rd, at what speed,? and on what ground , flat.?
the Trans measure speed and engine load. if the load is too high, (low vacuum weak engine) the trans will not go to 3rd, nor forth, unless you back the throttle, and load drops and it shifts.
so the load is too much.
that means weak engine, and low vacuum confusing the TCM


here is the chart that shows all shift points.

3rd can be as late as 60mph at 85% throttle (threshold)
or as low as 23mph.
as you can see a weak engine will in fact, make all shifting late. by design.

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with the TCM pulled, you will see , just like all 5sp sticks see, low engine power.

you didnt say engine misfires. so...
filter dirty from bad gas?
low fuel pressure.?
weak MAF (or just dirty.)
Bad fuel

is idle rpm hot at 800, and hods 800 hot , selecting DRIVE.????

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the 3 >4th shift, can happen at 80mph, (with too much TPS angle or engine load)