I think you're giving up too much. I don't play in any PPR leagues, so am unsure what the point system is per reception and whether or not WR's carry a team.
In the leagues I am in I have Stafford and Freeman and they are not not even close as far as fantasy points. Stafford could end up being an MVP candidate and fantasy stud and Freeman just seems like he's a winner when it comes to the NFL, but not fantasy. I actually regret taking him w/ Big Ben still on the board, bc I got caught up in the hype.
Also, Gore is one of those few RBS that get a serious bulk of the carries on his team. Of course he needs to stay on the field.
I know the injuries are a concern with the two, but having Mike Wallace and S. Johnson (pass happy Buffalo) seem like a pretty good group of WRs to go with.
I would offer Stafford straight up for Fitz and if the guy doesn't want it, just hope that Stafford keeps it up and I'm sure his opinion of the deal will change in a couple of weeks.
Since this is a PPR league and there is only one QB slot you're probably better off doing the trade. Top Tier WR like Fitz is more valuable in a PPR league than borderline tier 1/tier 2 RB like Gore plus you still can start Freeman.