I once fitted a bolt on cruise control unit made by Sears to a Shogun I had. That unit had a small electronic box of tricks with some adjustments in it. I would hazard a guess that either there may be adjustments in the Toyota box (mark or otherwise note their positions first before altering anything 'cos there may be more than one). So, and this would need help from one with higher knowledge than me, locate the cruise control ECU and try adjusting one adjustment at a time. Post a pic of location and of the unit and that will help. It may be possible to identify which bit to adjust (may need the lid off).
Alternately, swap it for a UK cruise control ECU.
Further than that I can't help as I haven't got cruise control on mine.…Would be nice to have though[emoji6] if anyone has the parts to add it S/H.