I have a concord seedless grape that I am growing in a container (for the first year or two) in the sunniest place in my yard. A week and a half ago I repotted it from its original nursery pot into a planter that has gritty mix. I also took the longest shoot and tied it to a stick. I have been watering it whenever the gritty mix feels dry about 3-4 inches down. The grape seems to be doing progressively worse. Last week was very cool (highs in the low 60s and now we are in the middle of a very unusual heat wave (it was 91 today and will be just as hot tomorrow). Some leaves are starting to shrivel. Is it transplant shock? Should I shade it?
Also, I haven't pruned it yet... I am trying to figure out exactly how to prune it. I think I should cut off all the shoots that are not part of the longest one that I tied up, but this will mean cutting off most of the leaves which makes me a bit nervous. Would pruning help it? Is that the right way to prune it?

Thanks in advance!
Robin

Here is a picture of my poor grape