Air bags do not increase GVW, they will level and improve the ride, but do not increase any weight limits. As for going to a F350 diesel that maybe a bit of overkill depending on how you make use of your truck on an everyday basis. Not only will your payments go up so will your maintenance and fuel cost. As may your insurance and registration cost. Most states base registration cost on the GVW of a vehicle over a set limit.
You could maybe get buy with a F250 6.2 gas V8 or look into loading your trailer and supplies lighter.
You could maybe get buy with a F250 6.2 gas V8 or look into loading your trailer and supplies lighter.