AU series 2 problems

[xrtonv]

hey guys ive been helping a mate try to fix his AU ute
back ground info
its a 2002 model 4l. with a 4speed auto
its a xls falcon ( long reach)
no it has a few problems
first!
it seems to be killing clusters,
the old cluster started frreezing up and sticking,( rpm ) and then starterd working backwards as in would rev out then when u got of the gas would stay at 6 or even 7 thousand
then as of today it started drove normaly and then all of the sudden bam the speedo went from 50km/h to 200km/h the rpm tacho stoped at 500rpm, the tempreture foze on hot and it was outa pertrol according to the guage.
so today we went to the wreakers (3rd time now) and changed it with a fully working unit
and it has started playing up agaian
so im guessing its electrical?
but where to start??

2nd!
The car seems to be missing on take off and generally down on power all accross the rev range
when accelerating from idel it stats to shake a lil and hesitate before it revs out
when in drive and accelerating from 50km/hr it feels asif the car dsont want to move
this has been happening for 3weeks or so now
we have changerd the following about a 2 months or so ago : spark plugs, leads, filter, o2 sensor, ran through a bottel of injector cleaner
and when ths was done the car was running insane but about 3 weeks ago it started these symptoms.
and now we are a lil stumpted

could the 2 problems be connected in anyway?
could the computer be fried? or something
what else is there to check
dimi
xrtonv