hiluxmad,
this may be a dumb question, but you are running the belt from the crank up to the tensioner and then over to the p/s alternator combo aye? (mine tensions fine and I don't have an alternator on the LHS (from front)).
I do recall in one of my 'blonde' moments trying to route the belt from the crank straight to the p/s alt and then round the tensioner up to the top central idler, could this be your problem?? (I couldn't find any good pics so see my 'mspaint classic' belt layout pic attached (obviously not to scale))
Muzz