Congratulations on your new, to you, truck! Regarding the seat cushions, I had that problem with my '03, 4X4 and what happened was after about an hour or more of driving, my right leg would start to really ache. Enough so that I just wanted to get out of it and walk around until the pain went away. I thought there was something wrong with my leg as I was getting older. I read of a fix for this problem on the TDR (what a great resource!!!) Basically, what you need to do (if you have the same seats as in the 4X4, is pull the seats out, take the upholstery off the lower part of the seat, pull up the thin foam and you will find a metal, wire gridwork (called a "ladder"), get a carpet sample and lay it over the wire gridwork (ladder), then get some 1/2" thick, closed-cell foam and cut a piece that fits that is the same size as the stock foam, and lay it over the carpet sample and put the upholstery back together. With the carpet sample, put the bottom side (burlap side) down on the wire with the fuzzy, carpet side up. Once the seat is put back together, it will bulge, slightly but, that is not a problem. The seat will be much more comfortable and I have never had a problem with it , again. Get the supplies at an upholstery warehouse. It didn't cost me much, at all. Probably about $20.00 for everything.
I, also, bought Covercraft Seatsavers (covers) for the front and backseats. Great purchase!!! They seem to wear well and if you get them dirty, I just throw them in the washing machine and re-install them. The last time I washed them, the stock upholstery looked brand new.
I put a large Caterpillar (Cat) fuel filter on my truck, also.
Also, use a Smarty Jr. and love it. As far as towing, on the "towing mode" (70 HP.) my exhaust gas temps. are always in the safe range and the extra power is nice. I think guages are a good idea and gives you something to watch while towing. Especially, if you get into the mountainous western US.
One of the problems I had was a knocking sound coming from the injectors or combustion chamber's. If you don't work the engine hard, occasionally, carbon can build up on the injector tips and diffuse the spray pattern of fuel into the combustion chamber and you get a knocking sound. No one at the dealership's I went to knew anything about the problem and wouldn't do anything to fix my problem. With the help of TDR members, they told me to either use a good fuel additive or just run the engine hard for a short while and it would clean up the carbon build-up. It worked well for me until the fuel additives started working. Simple fix!!!
I, also, have a 1991.5, W-250, 4X4 and like the '03 better. It is much more powerful, just as economical and, does everything I want it to do. I tow a 25' Nash 25-S bumper-pull travel trailer & I always have the 50gal. water tank full. I usually tow in the mountains of Arizona. It's normal to go from an 1100' elevation to around 9000' elevation in 5 hours of driving. The truck does very well pulling the trailer in those conditions. Truck and trailer have been through CA. OR. WA. NV. CO. WY. MT. AZ. NM. and as far east as Ontario, Can., MI. OH. IN. WV. & the states in-between. The truck has never broken down and left me on the side of the road. Very reliable and works as advertised!!!! Brakes are MUCH BETTER than those on the '91.5 W-250. I, also, had a Flowmaster, straight-thru muffler installed and like the extra sound quality of the engine. If you don't like loud Harley's, you may not like the extra sound. That's a personal matter!!! I love it!! Often drive with the radio off just to listen to the chorus of the Cummin's engine serenading me as I travel down the highway!!!!
Best of Luck with your new ride!!!
Buffalo