yes a first gen bed extender will fit a second gen, as long as you don't have the OEM bed cover. the bed cover brackets on the second gen trac will hit the 1st gen extender when flipping it out.
We got the "new" '08 Limited the other day and the bed extender from our '05 Adrenalin fit just fine. It doesn't even hit anywhere when rotated from one position to he other. I'm pretty happy about that. Both our Tracs had the factory hard bed cover as well.