I ferment my Kolsch at 58F and get 80% attenuation, without using adjuncts. The main factor is the mash, I do a 90min mash at 148F.
As for the Belgian style tripple, the yeast likes to start cool and warm up, by the end of fermentation it should be around 75F. The cool temperature could be the cause of the poor attenuation in the beer.
You said you aerate well, but do you pitch plenty of healthy yeast?