At 55 mph you are moving enough fuel so it shouldnt
be boiling... you might want to look at the fuel line
routing and see if its in contact with the block or
any other heat source.. when I worked on the fuel
boiling issue on production Chrysler cars, we would
see it boil out the bowls and dump raw fuel down the
intake while in a hot soak(engine off) and as soon as
the engine fire up and the driver would try a hard
acceleration it would stumble and/or die...and after
about 20 to 30 seconds it got enough fuel passing into
the bowls to cool them off so it wouldnt boil it..
then it drove fine... so driving at 55 it shouldnt
have been the boiling issue BUT you could have a pump
issue... do you run a return line with a vapor separator
near the carb