How do I use a newer version of jQuery with Ubercart shipping quote (Ajax)?
As it turns out, Ubercart will NOT work with jQuery after 1.2.6 unless you make a small change to an Ubercart module

ubercart/shipping/uc_quote/uc_quote.pages.inc

Go to around line 70 which should be the end of the uc_quote_request_quotes function

comment out or replace the broken drupal_json($return_quotes);

replace it with the standard PHP json encoder
print( json_encode($return_quotes) );