These AW7x transmissions are fairly bulletproof and can put up with a fair bit of abuse and poor maintenance. With any luck, a transmission fluid change using a good synthetic ATF followed by adjusting the kickdown cable may be all that's really needed to make an improvement. Choose a good multi-purpose Dex/Merc ATF like Valvoline Maxlife Multi-Vehicle Dex VI/Merc LV that's reasonably backwards compatible with the original Aisin-Warner specified Dexron II or III. Dex II/III have a slightly thicker viscosity than a single grade Dexron VI ATF formulation.
With an unknown history, ideally you'd want to do a full drain, drop the trans pan to inspect/clean the sludge, inspect/clean/replace the trans filter and follow that by a re-fill then a gentle flush using 2-3 times the normal amount of fluid until it runs out as clear as new fluid. The amount of grey sludge in the filter, on the bottom of the pan and especially on the magnet(s) can give you a clue of the condition of the trans and how well it's been looked after. If you start early and drain the pan a few times over a period of a few days or a week then you can often get an extra litre or so of old fluid out before you drop the pan. If the pan was wall to wall sludge then consider doing another flush after a few months of driving.
Now having said all that, with 940s it's much easier said than done to drop the trans pan. I would highly recommend you at least start with a gentle flush at the transmission cooler return line on the rad to see if that will help. It's very easy to do and doesn't even require the car to be jacked up to drain the pan first, although that may do a slightly better job and cut down on the amount of new fluid used. Give it a few weeks of driving before deciding how much of an improvement that makes. Just to give you an idea of how difficult it can be to drop the pan, the filler tube on the side of the pan is often impossible to get off without damaging the pan. You'll typically be faced with two choices, either removing the top starter motor bolt so you can free the filler tube and drop the pan with the tube in place, or cut the filler tube in the middle of the lower straight section so you can drop the pan with a stub of tube attached (mend it later with a brass double compression fitting, commonly available for under $10). But even worse with the later 940s is an exhaust support bracket blocking access to the rear screws of the pan. The engineer who designed this bracket ought to have been shot. To remove that bracket you need to remove the large cross brace and the entire transmission mount assembly off the back of the trans (requires an impact wrench or use of an extra long breaker bar). Trying to bend the bracket out of the way can easily damage the pan (plus it's hard to bend it back with the bolt lined up again). Putting the pan back on can also be frought with difficulties such as fluid leaks if the pan flange is warped/damaged from prying or the bolts being overtightened, also if a cheap gasket is used or if gasket cement/sealer is used incorrectly.
The main reasons to drop the pan are to replace the transmission filter or replace the kickdown cable. These AW trans filters rarely need to be changed. As long as you do semi-regular transmision fluid changes every hundred Kmiles or so then you can often go the life of the vehicle without needing to replace or even clean it. Although it never hurts to replace the trans filter, it's not a wear item. It's rarely plugged, leastwise to the point of being an issue. Volvo no longer specifies a routine service interval for the AW trans filter (a service bulletin was issued). It's to be replaced if and when needed or when you have the pan off for other reasons. You can usually clean and re-use the existing filter as long as you're careful not to damage the gasket during removal. You can flush it with something like spray brake cleaner if needed. Service manuals call for replacing the filter mostly because it's simply not worth the mechanic's time trying to clean it properly and the gasket can easily get damaged if you're not careful.
Your kickdown cable probably needs to be checked/adjusted. You need to do it in a quiet area and preferably after a tranny flush so there's no (or at least minimal) grunge in the bottom of the kickdown chamber. The proper adjustment is to loosen the cable until you can hear the kickdown pawl on the end of the cable hit the bottom of the kickdown chamber down in the trans when you pluck and release the cable (a faint clunk). You then adjust the cable tighter until the clunk can no longer be heard then secure the lock nut. You can go a few adjuster faces tighter or looser to get a bit more aggressive or slightly smoother shifting. When you pluck and release the cable, if the cable doesn't snap back smoothly all the way then the cable needs replacing (the cable frays, the internal sheathing wears through, binding and rusting). Note that in manuals you may see the kickdown cable adjustment shown as a .001-.04 mm gap between the little ferrule and the end of the adjuster. This should be treated as the initial adjustment. It's also only appropriate for the original factory cable. With replacement cables that little ferrule is clamped on by the installer who may or may not clamp it exactly where the factory would.
In case you're interested in the
approximate shift and lockup torque points, here's from the AW70/71/72 section of the Volvo 1991-1997 700/900 Pocket Data Booklet specifications:
Note that the lockup torque function is mechanical and speed related, not acceleration/load related. For your B230FK, your observed lockup happening at 100 km/hr is perfectly normal when you consider speedometer error, tire size/wear and the age of your trans.
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