'03 Ford F-250 with V-10 gas engine

thats a lot of tire ,wonder if it was used heavy off road??

I own a 2000 2 valve V-10 and they run good but fuel economy is not a strong point. I would not personally want to tow with a lifted vehicle, seems like it would be unstable at higher speeds. Then again I tend to push my vehicle's limits.

Others have already spoke about the exhaust bolts and plug issue. I had a trusted mechanic change the plugs and coils. I bought mine a with 169k on it.

I would also make sure the tires are load range E for towing.

Spark plugs should have been changed at 100k. Pricey if you have it done. Better job if Ford did it unless owner really knew what he was doing. My 410 towed better than my 373 differential did.

Check spark plugs, see when they were last changed. Can't tell you about longevity, but I know that is a very valued engine and will tow all day long (fuel tank permitting...).

Make sure the lift kit is high quality and that your payload and GVWR is not changed because of the kit. Other than that, you would just need to worry about buying a hitch with sufficient drop. My stock 2015 Ram is very tall and required me to purchase a 6" drop hitch in order to tow my trailer level.

I have an 01. Check the exhaust manifold bolts. They are prone to snapping the heads off the bolts and can be a pain to replace. I replaced them myself after several broke off and I got an exhaust leak. If it has 2 valve heads which I think it does, like mine, there are only 4 threads holding the spark plugs in. Some folks have had the motor spit out the plugs messing up the threads. I replaced my plugs and it wasnt a huge deal to do. Just torqued them very carefully. Despite the exhaust manifold bolt PITA repair I am very happy with the power train. Like you I live on a farm.My excursion fills in alot doing chores. I gets around 10mpg pulling my TT or livestock trailer. Does alittle better hauling hay with the flatbed.
Not sure about the 35s and a TT. I am sure someone will answer that.