I bought a 1991 F250 2wd 7.3E4OD new, it pulled ok but any grades or high elevation left it wheezing, never pulled over 8000 lbs behind it and that was a challenge. no mods ever
sold it and bought a new 96 F250 4wd with a 7.3PSD and ZF also 3.55s pulled excellent with no mods other than a turn down after the convertor/muffler removed, it pulled 12,000lbs easy and was willing for more. sold it to buy a house.
later in life purchased a 1990 F350 2wd dually 7.3 idi ATS turbo 3.5" downpipe and bumped up to 4" with a Nelson straight through muffler and turn down. it pulled ok with the 4.10s and 215s but was limited by hills with only around 200 hp. bought at 180,000km , headgaskets at 220,000. sold at 260,000 .could carry more than the stock 96 powerstroke maybe another 2000lbs because of duals but could never accellerate even in the same league. sold it to a buddy when I found my next worker. he still has the truck more than 6yrs later.
my present driver is a 2003 E350 extended clubwagon with seating only for 5. it has the 7.3 PSd and 4r100. only mod it an old 2 position superchip program on tow safe.
it had 360,000 km on it 6.5 yrs ago when I got it. according to last owner it was on its original injectors and turbo. I haul up to 12,000lbs behind it, including my 3000lb empty trailer. I have hauled more but with SRW and a semifloat 60 in the rear its a little shaky. power wise its not even maxed out at 14,000 lbs pull, and it has 3.55s and even an oversize tire 235/85/16s on it. at 540,000km last week it is still running on its original injectors and turbo. in 6 yrs I've doen waterpump twice, vacuum pump once, turbo up pipes and seals once, replaced a worn through steel fuel line under the turbo(3 months ago), 2 batteries (soon need at least one ) and a used starter.
anybody who has reliability issues with a 7.3 powerstroke has purchased one that hasn't been serviced or is not servicing it. use high quality oil and filters and only buy quality fuel!
I've owned both used and new and the powerstroke has been cheaper for me to run no questions
all my vehicles I drive hard empty and careful when loaded but I don't baby them. my friends say I drive them like I stole them
depending on the amount of loaded trailer driving you will be doing why not keep you idi and buy an older medium duty to haul your trailer? if you get one with hydraulic brakes your present drivers licence should be fine. and your loaded trailer won't be testing your braking limits.
reading through this thread there are some good ideas and advice .................... good luck on your decision.