5L-E: 3.0L 4cyl - 105BHP - 197Nm torque
2TR-FE: 2.7L 4cyl - 114bhp - 189Nm
1GRE-FE: 4.0L V6 - 236bhp - 361Nm
1KD-FTV: 3.0L 4cyl turbo - 172bhp - 352Nm
based on these basic numbers, if i were you
first off, i would cross the 2.7L Fortuner engine 2TR-FE off the list, as it is in the same torque range as ure current engine. it will be a total waste of good $ for nothing.
then we have remaining, the 1GR, 4.0L V6. something id throw in if im looking for a little speed on the stretches. will be heavy on the fuel, but only when driven hard. an over all a special engine to run.
personally id go for this as im a bit on the performance side of things. and who wouldnt love the sound a V6. but thats all personal and $ isnt an issue. as it would be costly to get purchase and get done.
and i wouldnt do it if i dont find a complete halfcut preferably with the driveshaft,diff and the whole drivetrain, everything to the wheel hubs.
lastly, the cheap and most economical change would be the 2KD-FTV. 3.0L turbo diesel. cant go wrong with it. same torque range as the mighty 4L V6 so ure looking at good fuel consumption, good off-the line feel, best for daily city driving.
cheaper to get done and easier to find than the V6.
and as again, wouldnot go ahead with the swap until i find a complete half cut. from the engine, to the diff.
just my 2 cents and how id go about it.