Did I kill my summersweet?

I planted a 'Sixteen Candles' (5 gal) about a month ago. I recently moved it and teased out the roots since it still looked very pot-bound. After replanting in a similar light/soil area, the leaves started to curl and look a bit crispy and the whole plant wilted. That same night we got a cold snap and it dropped down to the high 30s (not sure if this is pertinent but thought I'd mention it). I watered the shrub well before and after.

This is my first time caring for a clethra, so I'm not sure if I should be worried of if this is just your typical transplant shock? Before the move it was doing... ok. There was a bit of yellowing and leaf drop but I thought that might be because of the cooler temps. What should I be doing to make it perk back up other than monitor watering?

Being the time of year it is, I'm going to guess your plant has been sitting around the nursery since spring. This would have caused the 'very pot-bound' effect. Plants that are very pot-bound are at elevated stress levels because there becomes less and less soil to hold the moisture as the roots take over the pot. A plant like this will likely not transplant well. These are also plants that enjoy a moist soil and that will need to be provided through supplemental watering until leaf drop. I do think your plant is likely to be fine but it is probably shot for the rest of the year. Just keep up the water until leaf drop and then I'd leave it alone. Now next spring when it doesn't leaf out with everything else, don't be alarmed. These plants break dormancy late and, from what I remember, it doesn't produce leaf buds until it breaks dormancy. Good luck!

I dont know your zone so can only give a guideline, these plants like a milder climate, and do best in dapple shade in summer. they require a lime free soil so that means preferably acidic, IF your growing them in pots, you need to add plenty of peat / leaf-mould to the soil mix your using and it would help if it was free draining, even though these plants require lots of water, they don't like to sit in very wet soil for long periods of time. In winter IF you get really cold temps, it would be a good idea to take them inside for some frost protection BUT make sure you give enough light and water to just keep the plants alive.
in other words, dont allow the soil to dry out completely, soon as the temps begin to rise in early spring, sit the plants outside in day time and back in at night for several weeks to acclimatise them to the start of the growing season again. Once the plants get tooooo large for moving in and out end / start of season, you might need to find another type of protection when the plants HAVE to be left outside.
My way here in a windy, wet, cold climate in winter is to make a tent / wigwam type structure around the plants, either throw a couple of layers of horticulturaly fleece around the frame and secure it in place by making wire tent pins you stick through the fleece at the bottom and the pegs also get bedded into the soil OR, lay heavy stones in place to hold the fleece down. This very lightweight fleece allows some light through and water but it just prevents the wood from being either burnt or rotted with frost damage. a clear plastic cover laid the same way can help too but on bright days you need to open up the tent to allow air to circulate or the plants can get mould IF not careful.
I agree with Sequoidendron re the plants being suffering from neglect previously and they will suffer from shock for a short time now they have been re-potted, but just treat them with care for the first few weeks and they should recover, this is probably there winter resting period starting which is why you thought they looks poorly but you did the right thing by re-potting as end of summer-beginning or spring is the best time for that work to be carried out, the plants are going into dormancy or awakening depending on time of year, right now they wont be doing any growing with the exception of maybe recovery.
Hope this helps you out a bit.
Good luck and best regards.
WeeNel.