I personally haven't owned one, but my dad has had a couple. An '05 3/4 ton LLY and currently a '15 1-ton LML.
The '05 pulled an 14,000lb 5th wheel from coast to coast, up into the Rockies several times, Glacier NP twice, down to the gulf countless times, up to the UP of Michigan, and more. Roughly 35k miles of towing that trailer. Never once had a problem, and never once felt like we needed more truck, or more power. It did everything we ever needed it to. That truck was bone stock except we went up from the 245 tires to 265 tires. Other than that it was literally bone stock. Typically got around 8-9mpg towing if I recall correctly and would get 20+ empty. It was a phenomenal truck.
The '15 has pulled that same 14,000lb 5th wheel to Estes Park, Glacier NP, Durango CO twice, all over the smokies, etc. Roughly 10K miles pulling that trailer. They recently upgraded to an 18,000lb 5th wheel. They haven't had it long, but with that trailer the truck has gone to the Knoxville Nationals, Houston Tx, and Bristol, Tn. roughly 3K miles with the new trailer. Once again, haven't had any major problems, but the new truck is definitely more finicky with the sensors on everything. This truck is also bone stock except for a 60 gal. fuel tank. We have never felt like we needed more power or more truck.
The moral of the story, the trucks work fantastic in their bone stock form.
My opinion: Hundreds of engineers design these trucks, the engines, the transmissions, the transfer cases, the diffs, the suspension, etc. They are very good at what they do, and I have yet to find a reason for a street truck to be modified in any way. You have your race cars, and karts, leave the truck be. When you start to play around with the engine, you'll hurt the trans. When you fix the trans, you'll kill the rear end. Leave it be. If you want more power, buy a newer version of the truck.
Now if you want to make the thing a purpose built pulling truck or something, then go nuts I don't care.
Pic. for Proof
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