As a 2.8 GU owner myself, I'd advise you go the way of the 3 litre, just make sure it's at least 5 or 6 years old, younger would be better, but AVOID the 1999 thru to 2005 years, far to much grief.
Knowledge and parts are much more readily available for the 3 liter then the 2.8.
For what it's worth, my thoughts on the issue.

