You said it yourself, you stay witin 300 miles of home (300 miles would be an EXCURSION for me, LOL), and you do mostly local trips.
Just curious, but how many times per year does the rig leave your property? For me, I figure I MAY get out with it 5-6 times per year, at most. This is why I purchased an older TT so I don't have a payment on it and have all that money sitting there doing nothing, but to each their own of course.
My 00' Expy EB has a max tow rating of 6900 I think, my trailer's GVW is 6K with a 3500 "unladen" weight, so I figure fully loaded (I don't run with anything in any tanks) I'll be between 4500-5K. According to my owner's manual my GCWR is 12,500. I don't know what my Expy weighs but I'd suspect somewhere around 5500-6K, it's HEAVY, LOL.
At any rate, it does work hard on the hills/grades, but my point in all this is that for 5-6 times per year I'm not worried about it. A 2500 series truck with 4.10's would pull it a lot better and I will buy one when I'm ready for another TV, but for the time being I'm happy with the performance and having NO payments. For 6 times per year it can work hard, it does have the factory ford heavy duty tow package. If it breaks, I'll fix it and move on, if it's a major component failure, I may make the move at that time, but it's still pretty stout for it's age and 108K miles.
How much better will you feel about things with a 2500 series truck if you have a payment on it, or a larger payment than you do now? Is it worth it? Only you can answer that question, it's all personal preference as long as your within the limits/ratings of your TV.
My rig is 23' ball to bumper and it's older so it's heavy for it's size and I would not want to tow much more with my 00' Expy. The Layton pretty much has it at it's limits as far as I'm concerned.
YMMV,
Greg