I bought my '87 wagon with the exact same symptom. It was low on tranny fluid. I did the flush with a total expense of $15. Runs like a champ.
It really is very easy and gives you a sense of empowerment (sorry that pun slipped, oh, there I go again, and again...)

Good luck!
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Happy Motoring Miguel '86 244 and '87 245

Is it definitely slipping, or just not shifting? If it is slipping, there isn't enough fluid in it, or it is trashed. Those are about the only two common scenarios for slipping AW70s. You can run them low on fluid once, even twice (to the point of slipping). Usually the third time is the end.

However, the "near freezing" part makes me interpret "slipping" as "not shifting". This is from a long time "interpreting" customer problems. I immediately think about the kickdown cable. They tend to crack and get water in them. That leads to sticking... and at that point the trans doesn't shift. It isn't slipping, but it isn't shifting either. You can easily see if this is the problem by turning the throttle spool with the engine off and the car cold (after sitting all night in freezing temps especially). If it is freezing outside, the cable won't return. If this is true, then that is probably the issue... or at least AN issue.

Keep in mind that if it is truly slipping, don't drive it until it is warmed up and not slipping. That will eventually kill it.

Also, apologies in advance if your diagnosis is correct, but when the kickdown cable sticks, it can feel very strange, like there is a more serious problem with the transmission.

Are you sure you've got enough fluid in it? It sounds like a low fluid problem. Always check the dipstick with the transmission warmed up, and the engine running.
The fluid flush ought to be sufficient. The filter change is generally unnecessary as Volvo uses a mesh screen that reall doesn't need service. The flush you can do yourself, without even getting under the car- see the 700 FAQ, it's exactly the same procedure.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 230K, 88 744GLE- 220K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 94 855GLT 189K