Interesting problem with a transmission I'm not overly familiar with and we don’t hear about often in this forum. I’ll make a couple of general comments in case they help.

In the FAQ, the “Abe Crombie” reply to generally erratic AW30-40 shifting problems may be your best lead. Jim is/was a top Volvo Vista Master Mechanic and one of our top contributors here in the early years. His diagnoses were always pure gold so I would say the odds of it being a worn/faulty TPS are high. Short of having a scan tool to better diagnose the issue, I would want to electrically check out the TPS to make sure it’s functioning as expected and not at all having intermittent or irregular resistance throughout its range of travel, possibly even replacing it on spec with a good used one if I remained in doubt.

Second, it seems yours is not a problem with actual shifting, only a problem with the lockup torque converter kicking in and out when you're at the approximate lockup speed. With the AW7xL trans I’m more familiar with, the lockup function is hydraulically determined and controlled. There is a magic road speed where the trans will seemingly “hunt” in/out of lockup until your speed stays steadily above or below that point. A certain amount of that is normal, even though the behaviour seems unusual. I'm not sure if that's exactly what you're describing. Is your behaviour something that may have been there all along that you didn't really notice until now? I say that because even though gear shifting is electronically controlled in your AW30-40LE, it may be that the lockup torque converter is still completely hydraulic and worn/dirty valving/passageways might then be your issue rather than electrical.

And last, but by no means least, whenever any of us have unusual trans behaviour, the first thing we should be thinking of is a trans fluid flush. When was that last done? As much as Volvo stopped calling for regular trans fluid changes, many of us still consider 100K-150K miles a good change interval. The longer this has been left and especially if the trans has led a harsh life, or extremely high or extremely low miles, then be sure to thoroughly flush and maybe even repeat the flush a few Kmiles later. You may want to look into the pros and cons of switching to synthetic fluid or possibly even doing a pre-flush with something formulated for loosening trans fluid grunge (not that I at all generally recommend using such agents). There may also be an internal filter that might need cleaning/replacement if the trans is really grungy. Note that flushing should be done through the trans cooler lines until it runs perfectly clear, not simply draining and refilling. Ideally you begin by draining the pan and re-filling to get as much of the grunge out of there as you can initially, but many of us choose to skip the extra effort and mess and do a longer flush instead.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now