Have the spoke tensions checked, it is not uncommon for a mechanic to just true a wheel and not try to figure out why it went out of true. Low spoke tension could simply be the problem. If the spoke tensions are very uneven there is a good chance the rim was bent at some point and uneven tension is the only way to keep it true, this could also be part of the problem and if that is the case you should have a new rim laced to your old hub or have an entirely new wheel built (you can use spacers to make 7 speed work)

The CXP 33 is a good rim but there are stronger out there and for less money. If your roads are as bad as you say they are, over building is not a bad idea, especially if most of your miles are commuting. I personally would recommend looking at the Velocity Deep V, it is probably one of the strongest rims on the market that will work well with 23mm tires and is still very affordable compared to a lot of offerings from Mavic.