For a while now my transmission has only been able to shift manually for about the first mile of travel when cold or if it sits for more than a couple of hrs.
I drove it that way for a while. Now it only shifts manually all the time and I have to shift from 2nd straight to overdrive. It won't shift to 3rd but stays in second gear until I shift to OD. Then I do have OD.
Thanks in advance for any advice.

 

OK. Hijacked with no answers for the OP. Anyhow. Somehow my tranny has again started to shift correctly. It has done this several times since I bought the aerostar 12 yrs ago. Now that it shifts good I am thinking of doing a complete flush. While in there what else should I check which could cause me to have to shift manually for first mile of travel. That has been my most common on again off again problem for 12 yrs. I'm just glad I never took it to a shop. They probably would insist on rebuilding and I have got 12 yrs without rebuilding and it keeps going. 12 yrs so far on a $1000 vehicle. I ain't complaining and I'm confident I'll get a few more.

 

Before you do a complete flush, I would recommend a dose of Sea-Foam TRANSMISSION Treatment,not the motor treatment.
Takes about a can and a third for proper treatment. This will condition the tranny parts and seals and THEN do the complete flush. That's what I'd do anyway. don-ohio

 

When you replace the tranny filter, retorque the bolts on the valve body, about a dozen. They loosen over time and gasket can blow out causing erratic no shift. Best to replace gaskets but not for the weak of DIYer mechanical skills. Use ONLY the screen type filter, pad type plugs and kills tranny.
Do a complete gentle flush, search forum, takes about 20 quarts. Run line from front cooler into drain pan, run motor at idle, pour new tranny fluid in fill hole until clean pink ATF comes out into the pan.
For long tranny life use Mobil 1 ATF, does not break down in the high heat A4LD series.

Did mine about 15 years ago, still performs strong and never had to touch it since, never misses a shift, smoooooth. Mobil 1 is titty pink and only ATF odor only still.

Time to replace the side mounted vacuum modulator, the rubber diaphram in these only lasts a few years

 

Sounds like possibly an intermittent vacuum modulator (if your is mid-'95 or older). Mine failed in the opposite direction: early, too-shoft shifts.