Opinions of the 6.5 diesel vary.
As far as the logistics, the chassis is identical, gear ratio is 3.73 and should be fine as well. The computer and wiring needs to be swapped, but it appears that it only needs to be swapped external of the cab. The transmission is identical, except the diesels uses a separate TCM where the gas trucks have it integrated. The things that may be tougher problems are the AC lines are different, fuel lines may be different, fuel tank and sending unit are different, the dash cluster may be tough to make it “correct” but I think even those things will be fairly reasonable.
On older models or ones that had a 350 engine you would need to swap the torque converter and the brake booster.
The steering column may need to be worked on as well, something keys the column to the computer, I suspect it is some sort of resistance check, but I don’t know yet.