The ole stand by is a TST # 6 plate kit because its fairly usable with a decent turbo. The #5 will be hot depending on how far forward it is with the stock turbo. The 4K gov kit is interesting, mostly used for racing behavior. The 3K gov spring set up is more practical and won't cause valve float. I would not rev the crap out of an engine with that many miles and stock valve springs.
When towing the egt issue will be front and center, but with stock injectors you will be fine if you watch the gauge. I ran my old 160 hp truck with a #6, BHAF, stock injectors, 4" straight exhaust etc. for a while and I still had to back out of it when towing due to egt with a 10K arctic fox TT But, my 3.54 auto truck ran 900 degrees towing down the interstate with a #6.
My advice would be to keep the modifications conservative if your really towing often. Even with all my tweaking and HP I can't use 40 pounds of boost pulling hills loaded for long. The fun part is unloaded running, while towing I can't use the throttle much without hurting something. I personally use a BD valet switch when I'm in town towing, out on the highway I throw the fuel at it and control egt with my foot and gear selection.
I've ran mine for years at 1,000 to 1,100 degrees towing big trailers and the engine has survived great. My 1995 dually burns zero oil still. I back off the throttle at 1250 myself while loaded. Going to a larger turbo has its pros and cons, but when towing I can run 30 to 35 pounds of boost and stay under 1,000, but I stay above 2500 rpm when pulling hills. I don't regret spending the bucks on a big single turbo set up, but I always wanted a mild twin set up to loose the lag while solo.
Just make sure your turbo is healthy if you decide to add anymore fuel, you need air to burn the new fuel.