My understanding is that Fedex Freight is exclusively LTL at lower rates, while previously Fedex Ground/Express (now just Fedex) is potentially anything anywhere, but more expensively. Not sure if Fedex Freight ever had anything on the aircraft, as I suspect the rates to fly something LTL size would be astronomical. (Pricing out an LTL size package on fedex.com it looks like the LTL cost is roughly one fifth of the normal Fedex rate to send things via what would have been ground/express).