There is a problem in chronology with the Last Supper.  

Mat 26:17-29 and parallels in Mark/Luke place the scene where Jesus
tells his disciples to find the upper room on "the first day of
unleavened bread".  Mark 14:12 and Luke 22:7 equate this day with the
day on which the lamb is sacrificed.  The first day of unleavened
bread, technically speaking, is Nisan 15, Passover.  The day when the
lamb is sacrificed is the previous day, Nisan 14.  Albright and Mann
(AB Matt) quote Josephus as applying the name Unleavened Bread loosely
to the whole passover period.  They also say it is possible to
translate the Greek as "with reference to the first day of unleavened
bread", i.e. that they were asking about what should happen in
preparation for the next day.  Thus they and most other commentators
believe that the Synoptics envision this days as Nisan 14.  This
places the Last Supper as a Passover meal, since it occurs after
sundown, and thus on Passover, Nisan 15.  The crucifixion occurs on
the what we call the next day, but in Jewish reckoning is still the
same day, Nisan 15.  Mark 15:42ff and Luke 23:54 identify this as the
day of Preparation, i.e. the day before the Sabbath, Friday.  Of
course all the gospels agree that the resurrection was on Sunday
morning.

John 18:28, 19:14, etc., all imply that Jesus was crucified on the day
before Passover, Nisan 14, thus making the Last Supper (which was
after sundown, remember) also Nisan 14, i.e. not a Passover meal.  The
theological symbolism is interesting, since this would say that Jesus
was crucified as the Passover lambs were being killed.  There's no
disagreement over the day of the week.  John 19:31 makes it clear that
the crucifixion was on Friday, the day before the Sabbath, and John
20:1 again places the resurrection on Sunday morning.  (It's called
the third day, but remember that both Jews and Romans counted both
ends, so Friday to Sunday is three days.)

Thus the issue is not the day of the week, but the date, i.e.  whether
Passover was Friday or Saturday.  In my view we'll never know for
sure.  There are arguments for almost every possible view.  C.F.D.
Moule's commentary on Mark argues that the Synoptics are right, since
the Last Supper looks like a passover meal, which it wouldn't be in
John's scenario.  He thinks John made it a Passover meal for symbolic
purposes, to express the truth the Jesus is the true Paschal Lamb.
Raymond Brown argues that John's chronology is more plausible, because
the trial and crucifixion would not have occured on a major holiday.
John's picture of the priests needing to get this done before the
holiday starts makes more sense.  Under John's scenario, the Last
Supper would not have been an actual Passover supper, since it was a
day too early.  Yet it clearly has great similarities to a Passover
supper.  Maybe Jesus knew that he wouldn't be able to eat with them on
Passover itself, and so celebrated it a day early.  As a sort of early
Passover meal, Christian tradition could easily have gotten confused,
and come to think it actually was Passover, thus leading to the
accounts in the Synoptics.

There are also some theories trying to reconcile the two.  One is a
claim that there were calendars that differed by a day.  E.g.  it's
been claimed that the Palestinians calculated Passover by actual
observation of the new moon, and everyone else used a calendar.  So
they could be off by a day or two.  While this is convenient, there's
also no real evidence for it.  There is also a theory that Jesus kept
to the solar calendar used by the Essenes.  This is a complex theory,
resulting in a Last Supper on Tuesday, which was a Passover meal by
the Solar calendar, with a crucifixion on Friday, the day before the
Passover by the Lunar calendar.  Again, the evidence is very slim.
The passage used to establish this Solar calendar are ambiguous, it's
unclear why Jesus would have been following an Essene calendar, etc.

Basically my conclusion is that we simply don't have enough
evidence to decide.