I have a 95 3.8L Windstar with about 180,000 mi on it. It was runny fine before it sat for about 1 week in cold weather. When it started up is was runny very rough. The fuel tank was almost full so moisture in the fuel shouldn't have been a problem.

The tranny used to occasionally not want to shift from 1st to second under the following conditions:
1. If the car was started on a downslope
2. If you stopped quickly and then turned right fast.

To fix it you would have to shift into 2nd then back into drive and it would be fine. However now after sitting for a week it appears to be slipping in 1st gear. You can see the tach going up occassionally.

Is this a major fix or could it be something simple.

The tranny was rebuilt by Ford at 67,000 for the forward control valve that used to wear out.

I hate to get rid of the van, we've spent so much time together with me under the hood.

Sadly, the 1995 tranny was the worst in the lineup.
However.....your FORD repair may have addressed that issue.
However....it is STILL a 13 year old vehicle....and the other parts of the tranny are 13 years old.....with 180K miles on it.

A item that is known to fail......that is cheap and easy.....is the Transmission Range Sensor (TRS).
This same part is also called "Neutral Safety Switch".
The transmission is electronic controlled.....and a bad connection in one of the contacts inside the TRS can cause the transmission to not properly determine what you have selected with the gear selector.

ATF fluid changed regularly?....at least every 30K miles.
Mercon has been replaced by Mercon V......Mobil 1 ATF is a good one to use.....easy to find at AutoZone, etc.
I like to add some Auto RX, available at www.auto-rx.com 6 ounces 1000 miles before a ATF exchange.
I am NOT big on tranny fluid additives....but I have found that this product seems to GENTLY clean the clutch dust deposits from the fluid parts of the transmission.

I don't see the transmission causing the engine to run rough....so that may be a separate problem.
The 1995 3.8L is different from all the other year windstars as it does not have the "split port induction" with all the IMRC problems......
I would FIRST question any routine tune-up items....
Spark plugs
Spark plug wires
Air filter
Fuel filter
Coil pack
PCV (inspect the line from the PCV valve to the intake)
Clean MAF with non-residue electronic cleaner.
Check for vaccum leaks....vaccum lines and the flex line to the throttle body
Make sure that the oil breather line....from front valve cover to the back side of the flex line is in place.
Check the battery condition
Fuel system cleaner (Berryman's B-12 Chemtool)