My oil pressure is about 4bar cold then comes down to about 2.5 -3 when warm sounds ok to me missing could be plugs dizzy rota arm leads just check everything
dosent that ecu have a little black box to adjust the fueling ?? http://www.toyotagtturbo.com/forums/showthread.php?102843-Buddy-club-brack-box-pnp-ecu
if your rev gauge goes up but it doesn't seam like your going anywhere then yes your clutch is slipping and is most probably at the end of its life try it in 5th going up a hill if its going it will slip a lot then.